If e-mail messages from me appear blank on Microsoft Outlook: I sign my outgoing e-mails with GPG. Unfortunately, Outlook will display my responses as an attachment rather than the message of the e-mail. At this time, I am not aware of other clients exhibiting this kind of behavior.
If you are contacting me due to an issue on a URL that does not begin with http://www.presumed.net/~anton/ but it is from another user or page on presumed.net, you will want to contact that user instead. If it is not a user page, or not on presumed.net, you will want to contact the webmaster of the specific server, typically using e-mail messages. The webmaster e-mail addresses are typically going to be in a format such as webmaster@hostname.example.edu.
If you wish to send me a confidential message, you do not want to use e-mail, phone calls, or any other digital form for that matter. Digital communications are never truly going to be private, and multiple third-parties can always access the messages. End-to-end encryption is also worthless when there are backdoors into those encryption mechanisms.
If you are from the University of Akron, use your @uakron.edu, @zips.uakron.edu, or @1870.uakron.edu, unless we have already spoken enough times, and you've shared your personal or other professional e-mail address with me in person.
The most likely ones are that I either did respond but your system bounced due to a malconfigured spam filter, or I did not consider a response to be necessary. Either of our servers may have blocked the message for a number of reasons. If you are a friend, and you tried e-mailing me multiple times, it may be an issue with one of our Message Transfer Agents (MTAs). Checking the mail log files in /var/log/ should give sufficient information on what is going wrong in most cases.
Your e-mail messages should be sent either in English or with an English translation provided, written to the best of your ability. If I cannot read or understand your e-mail, I will not reply. While I do know people who can translate languages such as Spanish, German, Italian, French, Japanese, and Portuguese, among others, using this option will not be ideal for communications that involve sensitive information. Naturally, perse will understand what you wrote.
If you administer your own e-mail server, ensure that your machine can both send messages to and receive messages from 15.204.94.128 or 2604:2dc0:202:300::2187 (washington.presumed.net). If someone else administers the e-mail server for you, ask that person to ensure messages can be sent and received. This may resolve most issues that would be on your end. There is also the chance that I did receive your e-mail, was able to read it, and I was able to reply, but I just chose not to do so. Keep in mind that nobody is required to reply to every message they get.
Better yet: if your ISP or mailing service provider blocks this server's IP or domain, consider asking your ISP to stop blocking us on your account. To quote John Gilmore, a co-founder of the Electronic Frontier Foundation and the source I cribbed this section from, "Don't just let them put in an exception for mail from me. Get them to take off the blacklist on your incoming mail. It is usually hard -- but worth it. Who else's emails are you missing? Some of us figured out in the 1950s that blacklists were a bad idea."