There have been some delays with Discogs sending out mails over the past few days (sometimes delaying up to a few hours). This was caused by spammers trying to use our server to send spam. Even though they are blocked their constant attempts slow things down.
Today I set up a separate mail server dedicated to outgoing mail only. This does not accept any incoming mail so it should not be possible for outsiders to bog it down. Mail delivery should be back to normal now.