Many years ago I worked on the DPOP POP3 server and DList mailing list server, and did a little work on our company&#x27;s SMTP and IMAP servers too.<p>My experience was that most clients sucked.<p>For example, one (Eudora?) would move IMAP messages by copy and delete (which may have been idiomatic, as I say it was a long time ago). But it wouldn&#x27;t check the success of the copy operation, so a failure to copy would result in a delete, not a move.<p>Seems they still suck in 2016, for what seem like trivial reasons.<p>I mean, surely this sort of protocol interaction is very, very amenable to automated testing of some sort. We had a bunch of automated regression tests for our mail servers, written in C, back in the late nineties.<p>I&#x27;m genuinely uncertain whether to blame incompetence or another attempt at the strategies spelled out in the Halloween Documents: <a href="http:&#x2F;&#x2F;www.catb.org&#x2F;esr&#x2F;halloween&#x2F;faq.html" rel="nofollow">http:&#x2F;&#x2F;www.catb.org&#x2F;esr&#x2F;halloween&#x2F;faq.html</a>