I am wanting advice in securing an email server for large quantities of outbound emails daily.    Would like recommendations on hardware and software, plus cost estimates.   WOuld like system to grow with volume.   Starting out at 30,000 emails per day, and then growing from there.    Want to make sure my business plan can afford this.
This is a  about  Related:      I have a question regarding capacity planning. Can the Server Fault community please help with the following:   What kind of server do I need to handle some number of users? How many users can a server with some specifications handle? Will some server configuration be fast enough for my use case? I'm building a social networking site: what kind of hardware do I need? How much bandwidth do I need for some project? How much bandwidth will some number of users use in some application?
No upgrade available for 19.04 from 18.10 I'm pretty new to running linux, but I know that 19.04 was released today and I wanted to upgrade from my current 18.10. However, when I follow the release notes here:  I get the message "The software on this computer is up to date". I made sure that my update settings are set to "any new version" and "normal" in the /etc/update-manager/release-upgrades file.   What am I doing wrong?  Thanks for the help!  Side note: I had to disable this PPA:  because it would cause errors in apt updating. Do I need to re-add it? If so how do I do so without it giving me an error?  Edit: I have followed the procedure recommended in the documentation which is identical to the suggested duplicate, but I am not given the option to upgrade. I have not yet tried the   do-release-upgrade -d    option as I don't want to upgrade to the developer version. Why isn’t the definite article used in "The commission commanded that work [...] should cease"? In this sentence:     The commission commanded that work on the building should cease.   Why isn't the used before the word work? It seems that the work is specified by on the building.  Another example is,     Construction of the building will start next week.   I understand construction here is something like putting up the building, and so the construction isn’t general in meaning. But the definite article isn’t used here, either.  I’ve asked about this several times, but none gave me a good answer. Is it alright to use lowercase "i" or should you always use "I" (uppercase)? Weighing a flying bird This is a Q&amp;A so I answer it myself. I searched for an answer to this question for ages and didn't find anything so I'll add this here if anybody else struggles with the same issue.  So, how can I merge two edge loops to one? I do not want to connect them (I have seen many answers that suggest to just bridge the edge loops), nor do I want to merge each vertex by hand. I just want each vertex to be merged with the closest opposing vertex.  Also, I find it highly unpractical and in most situations useless to remove doubles after moving the vertices to overlap each other by scaling and moving the edge loops. This is another common suggested answer. 'innerText' works in IE, but not in Firefox Qualcomm Atheros AR9462 with Ubuntu 18.10 I can't enable the Wifi (nothing happens when press enable button) and in Wifi settings it says:     "No Wi-Fi Adapter Found"   I have tried several things from other questions/answers here but nothing worked. Here some information if this is helpful for the answer:     Device: Lenovo Miix 2 11   sudo lspci:  Network controller: Qualcomm Atheros AR9462 Wireless Network Adapter (rev 01)   sudo lshw -C network:  *-network DISABLED            description: Wireless interface    product: AR9462 Wireless Network Adapter    vendor: Qualcomm Atheros    physical id: 0    bus info: pci@0000:02:00.0    logical name: wlp2s0    version: 01    serial: 48:d2:24:8a:ea:e6    width: 64 bits    clock: 33MHz    capabilities: pm msi pciexpress bus_master cap_list rom ethernet physical wireless    configuration: broadcast=yes driver=ath9k driverversion=4.18.0-16-generic firmware=N/A latency=0 link=no multicast=yes wireless=IEEE 802.11    resources: irq:18 memory:f0400000-f047ffff memory:f0480000-f048ffff   sudo lsmod | grep ath:  ath3k                  20480  0 bluetooth             548864  12 btrtl,btintel,btbcm,bnep,ath3k,btusb ath9k                 151552  0 ath9k_common           36864  1 ath9k ath9k_hw              475136  2 ath9k_common,ath9k ath                    36864  3 ath9k_common,ath9k,ath9k_hw mac80211              794624  1 ath9k cfg80211              663552  5 wl,ath9k_common,ath9k,ath,mac80211   In system settings it shows the Wifi-Adapter Name:  Qualcomm Atheros AR9462   Edit:  lspci -knn | grep Net -A3; rfkill list:  02:00.0 Network controller [0280]: Qualcomm Atheros AR9462 Wireless Network Adapter [168c:0034] (rev 01) Subsystem: Lenovo AR9462 Wireless Network Adapter [17aa:3214] Kernel driver in use: ath9k Kernel modules: ath9k, wl 0: phy0: Wireless LAN     Soft blocked: no     Hard blocked: no 1: ideapad_wlan: Wireless LAN     Soft blocked: no     Hard blocked: yes 2: ideapad_bluetooth: Bluetooth     Soft blocked: yes     Hard blocked: yes How to extract and install .deb without the command dpkg? I am running Debian jessie stable in order to understand how the .deb package interacts with the system. What is the correct way to extract and install a packge_name.deb without the command dpkg? Finding an old flight number How can I find an old flight number from over three years ago? I am trying to make a claim for a delay of over five hours. They sent us to the wrong destination and lost our luggage. Received an email intended for another person Best Azure Service for Large no of SQLServer Databases The isomorphism $\mathbb{Z}[i]/(a+bi) \cong \Bbb Z/(a^2+b^2)\Bbb Z$ is , when the integers $a$ and $b$ are coprime. But what happens when they are not coprime, say $(a,b)=d&gt;1$?      — For instance if $p$ is prime (which is not coprime with $0$) then $$\mathbb{Z}[i]/(p) \cong \mathbb{F}_p[X]/(X^2+1) \cong \begin{cases} \mathbb{F}_{p^2} &amp;\text{if } p \equiv 3 \pmod 4\\ \mathbb{F}_{p} \times \mathbb{F}_{p} &amp;\text{if } p \equiv 1 \pmod 4 \end{cases}$$ (because $-1$ is a square mod $p$ iff $(-1)^{(p-1)/2}=1$).  — More generally, if $n=p_1^{r_1} \cdots p_m^{r_m} \in \Bbb N$, then  each pair of integers $p_j^{r_j}$ are coprime, so that by CRT we get $$\mathbb{Z}[i]/(n) \cong \mathbb{Z}[i]/(p_1^{r_1}) \times \cdots \times \mathbb{Z}[i]/(p_m^{r_m})$$  I was not sure how to find the structure of $\mathbb{Z}[i]/(p^{r}) \cong (\Bbb Z/p^r \Bbb Z)[X] \,/\, (X^2+1)$ when $p$ is prime and $r&gt;1$.  — Even more generally, in order to determine the structure of $\mathbb{Z}[i]/(a+bi)$ with $a+bi=d(x+iy)$ and $(x,y)=1$, we could try to use the CRT, provided that $d$ is coprime with $x+iy$ in $\Bbb Z[i]$. But this is not always true: for $d=13$ and $x+iy=2+3i$, we can't find Gauss integers $u$ and $v$ such that $du + (x+iy)v=1$, because this would mean that $(2+3i)[(2-3i)u+v]=1$, i.e. $2+3i$ is a unit in $\Bbb Z[i]$ which is not because its norm is $13 \neq ±1$.  — I was not able to go further. I recall that my general question is to known what $\mathbb{Z}[i]/(a+bi)$ is isomorphic to, when $a$ and $b$ are integers which are not coprime (for instance $a=p^r,b=0$ or $d=(a,b) = a^2+b^2&gt;1$).  Thank you for your help! Linear Discriminant Analysis for $p=1$ I'm studying 'Introduction to Statistical Learning' by James, Witten, Hastie, Tibshirani.   In page 139, of their book, they began by introducing Bayes' Theorem $p_k(X)=P(Y=k|X=x) = \dfrac{\pi_kf_k(x)}{\sum_{l=1}^k \pi_l f_l(x)}$. $\pi$ is not mathematical constant, but denotes the prior probability. Nothing is strange in this equation.   The book claims that it wants to obtain an estimate for $f_k(x)$ that it can plug into the equation given above. To estimate $f_k(x)$, it assumes that is normal. In the one dimensional setting, $f_k(x)=\dfrac{1}{\sqrt{2\pi}\sigma}\exp(-\dfrac{1}{2\sigma^2}(x-\mu_k)^2)$, where $\mu_k$ and $\sigma^2_k$ are the mean and variance for the $k$th class. It is assumed that $\sigma^2_1 = \sigma^2_2 = \cdots = \sigma^2_K$. (I began to get confused from the last statement.)   Plugging $f_k$ into $p_x$, you have this quite messy equation (1) :   $$p_x(k)=\dfrac{\pi_k \frac{1}{\sqrt{2\pi}\sigma}\exp(-\frac{1}{2\sigma^2}(x-\mu_k)^2)}{\sum_{l=1}^K \pi_l \frac{1}{\sqrt{2\pi}\sigma}\exp(-\frac{1}{2\sigma^2}(x-\mu_l)^2)}. $$  Again, no surprises here since it is just substitution.     The Bayes' Classifier involves assigning an observation to the class for which equation (1) is the largest. Taking the log of Equation (1) and rearranging terms, it is not hard to show that this is equivalent to assigning the observation to the class for which the following is the largest:  $$\delta_k(x)=x \cdot \dfrac{\mu_k}{\sigma^2} - \dfrac{\mu_k^2}{2\sigma^2} + \log(\pi_k) $$  Question: I do not understand where this came from, and what it means. I tried doing the log of equation and it doesn't become this. Are we taking the derivative somewhere here, since this is the largest observation? How can I move an object towards another along a straight line Auto.arima with daily data: how to capture seasonality/periodicity? I am fitting an ARIMA model on a daily time series. Data are collected daily from 02-01-2010 to 30-07-2011 and are about newspaper sales. Since a weekly pattern in sales can be found (the daily average amount of copies sold is usually the same from Monday to Friday, then increases on Saturday and Sunday), I am trying to capture this "seasonality". Given the sales data "data", I create the time series as follows:  salests&lt;-ts(data,start=c(2010,1),frequency=365)   and then I use the auto.arima(.) function to select the best ARIMA model via AIC criterion. The result is always a non-seasonal ARIMA model, but if I try some SARIMAs model with the following syntax as example:  sarima1&lt;-arima(salests, order = c(2,1,2), seasonal = list(order = c(1, 0, 1), period = 7))   I can obtain better results. Is there anything wrongs in the ts command / arima specification? The weekly pattern is very strong so I would not expect so many difficulties in capturing it.  Any help would be very useful. Thank you, Giulia Deppieri  Update:  I have already changed some arguments. More precisely, the procedure selects ARIMA(4,1,3) as the best model when I set D=7, but AIC and the others good of fit indexes and forecasts as well) do not improve at all. I guess there's some mistakes due to confusion between seasonality and periodicity..?!   Auto.arima call used and output obtained:  modArima&lt;-auto.arima(salests,D=7,max.P = 5, max.Q = 5)     ARIMA(2,1,2) with drift         : 1e+20  ARIMA(0,1,0) with drift         : 5265.543  ARIMA(1,1,0) with drift         : 5182.772  ARIMA(0,1,1) with drift         : 1e+20  ARIMA(2,1,0) with drift         : 5137.279  ARIMA(2,1,1) with drift         : 1e+20  ARIMA(3,1,1) with drift         : 1e+20  ARIMA(2,1,0)                    : 5135.382  ARIMA(1,1,0)                    : 5180.817  ARIMA(3,1,0)                    : 5117.714  ARIMA(3,1,1)                    : 1e+20  ARIMA(4,1,1)                    : 5045.236  ARIMA(4,1,1) with drift         : 5040.53  ARIMA(5,1,1) with drift         : 1e+20  ARIMA(4,1,0) with drift         : 5112.614  ARIMA(4,1,2) with drift         : 4953.417  ARIMA(5,1,3) with drift         : 1e+20  ARIMA(4,1,2)                    : 4960.516  ARIMA(3,1,2) with drift         : 1e+20  ARIMA(5,1,2) with drift         : 1e+20  ARIMA(4,1,3) with drift         : 4868.669  ARIMA(5,1,4) with drift         : 1e+20  ARIMA(4,1,3)                    : 4870.92  ARIMA(3,1,3) with drift         : 1e+20  ARIMA(4,1,4) with drift         : 4874.095   Best model: ARIMA(4,1,3) with drift           So I assume the arima function should be used as:  bestOrder &lt;- cbind(modArima$arma[1],modArima$arma[5],modArima$arma[2]) sarima1&lt;-arima(salests, order = c(4,1,3))   with no seasonal component parameters and period specifications. Data and exploratory analysis show that the same weekly pattern can be approximatively considered for each week, with the only exception of August 2010 (when a consistent increase in sales is registered). Unfortunately I have no expertise in timeseries modeling at all, in fact I am trying this approach in order to find an alternative solution to other parametric e non-parametric models I have tried to fit for these problematic data. I have also many dependent numeric variables but they have shown low power in explaining the response variable: undoubtedly, the most difficult part to model is the time component. Moreover, the construction of dummy variables to represent months and weekdays turned out not to be a robust solution. How do I pass a function as a parameter to in elisp? I'm trying to pass one method to another in elisp, and then have that method execute it.  Here is an example:  (defun t1 ()   "t1")  (defun t2 ()   "t1")  (defun call-t (t)   ; how do I execute "t"?   (t))  ; How do I pass in method reference? (call-t 't1) How to use articles with scientific words, such as mass, force, impulse, field and others? How are articles used with scientific quantities, such as mass, force, impulse, field and others? Finding Zero Divisors and Units of Rings $\mathbb{Z}_n \times \mathbb{Z}_m$ Applying MVT and IVT (?) to show something about f'''? (edit: actually, Taylor's Theorem using Lagrange remainder) I believe that the correct answer to this question will involve applying both the Mean Value Theorem and the Intermediate Value Theorem, perhaps several times.  However, I can't see how to proceed.  I went down what I thought were the typical paths and just reached dead ends.  Does someone maybe have a hint?  I think that with the appropriate nudge I should be able to solve this question.  If not, I'll edit and ask if someone knows how to solve the whole thing.  Here's the question:  Let $f: \mathbf R \to \mathbf R$ be such that $f$, $f'$, $f''$, and $f'''$ exist and are continuous on $\mathbf R$ and satisfying $f(-3)=-1$, $f(0)=0=f'(0)$, and $f(3)=8$.  Prove that there exists $\xi \in (-3, 3)$ such that $f'''(\xi) \ge 1$. This morning, I read Wikipedia's informal definition of a limit:     Informally, a function f assigns an output $f(x)$ to every input $x$. The   function has a limit $L$ at an input $p$ if $f(x)$ is "close" to $L$ whenever   $x$ is "close" to $p$. In other words, $f(x)$ becomes closer and closer to $L$   as $x$ moves closer and closer to $p$.   To me that sounds like something that might be better described as a 'target'.  If I take a simple function, say one that only multiplies the input by $2$; and if my limit is $10$ at an input $5$: then I've described something that seems to match the elements contained in Wikipedia's definition. I don't believe that that's right. To me it looks like an elementary-algebra problem ($2p = 10$). To make it more calculusy, I could graph the function's output when I use inputs other than $p$, but that really wouldn't give me anything but an illustration of the fact that one's answer moves farther from the right answer as it becomes more wrong (go figure).   So limits are important; what I've just described is trivial. I do not understand them. I know calculus is often used for solving real-world challenges, and that limits are an important element of calculus, so I assume there must be some simple real-world examples of what it is that limits describe.   What is a simple example of a limit in the real world?  Thank you  -Hal.