The situation:   Even though SPF, DKIM, and the entire mail formatting is optimized to score 10/10 on , many outgoing mails are marked as spam in yahoo and outlook. The primary server sends out the emails. Incoming email is handled with mailgun.org, so the MX records (on the primary server) point to mailgun servers.  It is relatively easy to set up the PTR record for the primary server, but AFAIK impossible on mailgun.   Questions   Is setting the PTR record on the primary server enough?  If not: what is the exact way a major email service provider checks incoming emails regarding the PTR record?   a) domain -> read MX record -> look up PTR of domain in the MX record (which would be mailgun)  b) domain -> look up PTR record of that domain (primary server in this case)  c) other?
This is a  about how to handle email sent from your server being misclassified as spam.  For additional information you may find these similar questions helpful:                    Sometimes I want to send newsletters to my customers. The problem is, that some of the emails get caught as spam messages. Mostly by Outlook at the client (even in my own Outlook 2007).  Now I want to know what should be done to create "good" emails. I know about reverse lookup etc., but (for example), what about a unsubscribe link with an unique ID?  Does that increase a spam rating?
Surjective morphism of affine varieties and dimension I'm trying to do the following exercise from the book An Invitation to Algebraic Geometry:     Show that if $X \to Y$ is a surjective morphism of affine algebraic varieties, then the dimension of $X$ is at least as large as the dimension of $Y$.   Could anyone give me a hint? I'm looking for a proof that avoids commutative algebra since it is not mentionned in the book at this point. Most OO languages prefix their interface names with a capital I, why does Java not do this?  What was the rationale for not following this convention?  To demonstrate what I mean, if I wanted to have a User interface and a User implementation I'd have two choices in Java:        Class = User, Interface = UserInterface   Class = UserImpl, Interface = User      Where in most languages:     Class = User, Interface = IUser   Now, you might argue that you could always pick a most descriptive name for the user implementation and the problem goes away, but Java's pushing a POJO approach to things and   most IOC containers use DynamicProxies extensively.  These two things together mean that you'll have lots of interfaces with a single POJO implementation.  So, I guess my question boils down to: "Is it worth following the broader Interface naming convention especially in light of where Java Frameworks seem to be heading?" What command do I need to unzip/extract a .tar.gz file? I received a huge .tar.gz file from a client that contains about 800 mb of image files (when uncompressed.) Our hosting company's ftp is seriously slow, so extracting all the files locally and sending them up via ftp isn't practical. I was able to ftp the .tar.gz file to our hosting site, but when I ssh into my directory and try using unzip, it gives me this error:  [esthers@clients locations]$ unzip community_images.tar.gz Archive:  community_images.tar.gz   End-of-central-directory signature not found.  Either this file is not a zipfile, or it constitutes one disk of a multi-part archive.  In the latter case the central directory and zipfile comment will be found on the last disk(s) of this archive. note:  community_images.tar.gz may be a plain executable, not an archive unzip:  cannot find zipfile directory in one of community_images.tar.gz or community_images.tar.gz.zip, and cannot find community_images.tar.gz.ZIP, period.   What command do I need to use to extract all the files in a .tar.gz file? Why do my LED lights stay on, even when the switch is off? How can I copy a file from another directory to the current one? I have this problem as part of a school assignment:  NOTE: In case it's hard to read in the image above, here's the directory tree: $ tree . `-- sample_dir1     `-- sample_dir         |-- admin         |-- cambridge         |   |-- cafeteria         |   |-- library         |   `-- security         |       |-- annex         |       |-- building         |       `-- parking         |-- faculty         |-- history.exe         |-- markham         |   |-- annex         |   |-- building1         |   `-- parking         |-- oxford         |   |-- outline.doc         |   |-- programming         |   |   `-- report.pdf         |   `-- security         `-- stenton             |-- gen_ed             `-- lib_arts                 |-- english.txt                 `-- match.doc  15 directories, 11 files  I tried doing the command: $ cp ../cambridge/security/parking ./parking2  ...but it isn't working. The question in the image above states that the current directory is stenton, and that we need to make a copy of the file named parking (from the security directory), and to name the new file parking2, and place it in the current directory, stenton, using relative pathnames. What am I doing wrong? My cp command seems to be correct. "Open With" dialog ignores my selection I need a compact representation of an array of booleans, does Python have a builtin bitfield type or will I need to find an alternate solution? Prove divisibility law $\,b\mid a,c\,\Rightarrow\, b\mid ka + lc$ for all $k,l\in\Bbb Z$ Why “which” returns none on some commands I can run? SD Card showing weird file names and files are lost I just plugged my SD Card to my PC after a long videography day, and I suddenly got this problem:    It is also not showing all the videos I took on my camera so what is the solution? booting windows 10 spends too long In august 2015, I have upgrade my laptop from windows 8.1 to windows 10. But it spends always 10 minutes to boot it. It is not normal that it spends so long. What can I do for boot him faster? Below some information about my laptop.   age: +/- 2 year (on august 2015) edition: Windows 10 Home   File trace are removed.  Update:    I must also say that always there comes a windows update, I have the same problem again form slow booting. Is it good that I turn off the updates? If yes, how can I do that? Also it is in periods that my pc booting to slow. Some time it is like normal (a few seconds) and other times a few minutes. I don't know how it comes that it is fast or slow. Unable to lock the administration directory (/var/lib/dpkg/), are you root? I get this error in Lubuntu 12.04 when I try to update in terminal:  $ apt-get update E: Could not open lock file /var/lib/apt/lists/lock - open (13: Permission denied) E: Unable to lock directory /var/lib/apt/lists/ E: Could not open lock file /var/lib/dpkg/lock - open (13: Permission denied) E: Unable to lock the administration directory (/var/lib/dpkg/), are you root? Where are some places to get reference images for modeling? I'm a newbie.  I've gone through a number of tutorials and want to get some actual experience with modeling. But, I don't know where to go to get good reference images for modeling with front/sides views.  Can anyone recommend the best places to find such images? How can I prove that the additive group of rationals is not isomorphic to a direct product of two nontrivial groups? I am working through Paolo Aluffi's new GSM text on my own (self-study). On page 63, he asks the reader to     Prove that $\Bbb{Q}$ is not the direct product of two nontrivial groups.   For some context, this is an exercise following a section entitled "The category Grp".  I am assuming that he means "is not isomorphic to the direct product of two nontrivial groups", and I can see two possible ways to proceed with this proof, but have been unsuccessful with either approach.    Approach 1:  Show that the additive group of rationals has a property that is preserved by isomorphism that the direct product of two nontrivial groups does not have or vice-versa.  This seems challenging unless I can significantly narrow down the properties that a direct product of two nontrivial groups that was isomorphic to $\Bbb{Q}$ would necessarily have.  Approach 2:  Considering the section in which this question occurs, show that if $G$ and $H$ are nontrivial groups and $\Bbb{Q} \cong G \times H$, then there are homomorphisms $\varphi_{G}:\Bbb{Q} \rightarrow G$ and $\varphi_{H}:\Bbb{Q} \rightarrow H$ which do not factor or do not factor uniquely through the product $G \times H$.  This would be a contradiction, as $G \times H$ is a final object in the category Grp.  I would greatly appreciate suggestions on how to proceed further with either of these approaches or with alternate approaches. Why does this PNG image on twitter look different when clicked? This morning on twitter there was a tweet with the text "click on this picture".  When picture is clicked, it's opened in wider viewer, but looks completely different.  I tried to analyze this picture in ACDSee, and I also tried uploading on Facebook, but it's happening only when embedded on twitter. I don't have much knowledge about graphics so please explain this to me. Why does this PNG image change only when clicked on Twitter?  Screenshots (left = before clicking; right = after clicking):     Here's the original . How can I install firmware-b43-installer driver if I can't connect to internet by wire? Elements of $\mathbb Q(2^{1/3})$ How does DC work with natural 20? \nameref breaks for the star versions of section, paragraph when titlesec is loaded. I have a document that numbers paragraphs by default, but I have a few I do not want to number but would like to refer to. These are marked with \paragraph*, however, if the titlesec package is loaded at the same time, it causes nameref to display an empty string (the link box of hyperref is still visible).  MWE:  \documentclass[12pt]{article} \usepackage[sf]{titlesec} %comment this out and it works fine. \usepackage{hyperref} \begin{document} \section{Sections} \label{sec} This is \nameref{sec} \paragraph{A named Paragraph} \label{par} This is \nameref{par} \paragraph*{A starred named Paragraph} \label{par:star} This is \nameref{par:star} \end{document}   I suspect titlesec causes this defect for ALL star variants of sectioning commands but have not tested this. For me only paragraph* is relevant however a fix for all variants would be the best.  I have a hunch it might be related to this:  however this happens to go way beyond my latex knowledge and is just "magic" for me. Floating Objects and Weight The Situation:  A ball is placed in a beaker filled with water and floats. It is also attached to the bottom of the beaker via a string.   The Question:  The ball is attached to the beaker, thus making the ball and beaker (and string included) a system. However, it is floating. Does the ball add to the weight of the beaker?