Database mail trying to send 2 times and then failing

Our database mail was running for 3 years without problems, but since one week, we are often (but not always) getting this error:

The mail could not be sent to the recipients because of the mail server failure. (Sending Mail using Account 1 (2021-10-13T22:31:21).
Exception Message: Cannot send mails to mail server. (Failure sending
mail.). )

Unfortunately this message is not very helpful. Database mail is always trying to send the mail 2 times (with 1 minute interval), then it finally fails.

• Is there a way to find out why exactly it is failing? ?

• Is there a way to reconfigure database mail, so that it tries more often or sends in other ways?

I discovered this week that we have been having the same problem. It started really around 10/1 and had been on and off, but not serious enough to come to my attention. This week, though, it had gotten much more severe. Yesterday I couldn't get a single email out from any of our 3 DBs, all routing through SMTP at Office 365. You don't mention your SMTP, so this may or may not be the issue for you.

Doing some digging, the one fix I could find that I believe addresses this issue is here: https://dba.stackexchange.com/a/233249/131993

Once we used that registry executable on the machine with SQL Server I was able to reliably send email on the first try. I sent around 150 messages after that fix with no issues. Because it's intermittent, I can't say with 100% certainty the issue is fixed, but so far it looks good.

StackExchange Database Administrators Q#301122, answer score: 4