Hello, the problem is not emacs related: I just tried with swaks and it displays the exact same problem.
Swaks session: hobbes@sphax:~$ swaks --to r...@lybrafox.be --from hob...@poukram.net --server localhost === Trying localhost:25... === Connected to localhost. <- 220 sphax.lybrafox.lan ESMTP Exim 4.94 Fri, 19 Jun 2020 21:09:05 +0200 -> EHLO sphax.lybrafox.lan <- 250-sphax.lybrafox.lan Hello localhost.lan [::1] <- 250-SIZE 52428800 <- 250-8BITMIME <- 250-PIPELINING <- 250-X_PIPE_CONNECT <- 250-CHUNKING <- 250-STARTTLS <- 250-PRDR <- 250 HELP -> MAIL FROM:<hob...@poukram.net> <- 250 OK -> RCPT TO:<r...@lybrafox.be> <- 250 Accepted -> DATA <- 354 Enter message, ending with "." on a line by itself -> Date: Fri, 19 Jun 2020 21:09:05 +0200 -> To: r...@lybrafox.be -> From: hob...@poukram.net -> Subject: test Fri, 19 Jun 2020 21:09:05 +0200 -> Message-Id: <20200619210905.142...@sphax.lybrafox.lan> -> X-Mailer: swaks v20190914.0 jetmore.org/john/code/swaks/ -> -> This is a test mailing -> -> -> . ===== 20 seconds delay is here ===== <- 250 OK id=1jmMNt-000b8d-Al -> QUIT <- 221 sphax.lybrafox.lan closing connection === Connection closed with remote host. The problem might be related to https://lists.exim.org/lurker/message/20200619.090409.faf4b641.en.html But if the unique identifier in question is the message id, it immediately appears in the log *before* the delay, so the reason is not the id. Also, exim 4.93 does not have a problem when my laptop sleeps, and I guess it would have the same problem if my clock moved backwards, so while the explanation might be there somewhere, the exact reason is different. Also, my clock certainly does not move backwards, I would see it. But maybe the clock in question is not what I see on my desktop ? Thanks for your work, -- Rémi