Does it happen mainly when sending a message to multiple recipients? (vs a single recipient)

Does it happen less in Windows safe mode? https://support.microsoft.com/en-us/help/12376/windows-10-start-your-pc-in-safe-mode

Single or multiple messages get SMTP timeouts, but messages send OK. This started right after the update as best I can tell. I use filtering and it occurs when a message received and forwarded by filter action.

Have different accounts and occurs on both servers so it seems the update is involved.

> I use filtering and it occurs when a message received and forwarded by filter action.

Only when filters are involved?

It appears that is the case. Will figure out a test to see. Usually it takes a few seconds for messages to pop up after activity. Will watch when messages come in to see if it's only the filter actions on the incoming messages that have filters. A test may help determine.

Sent message from account(A) to account(B) and no message. Created filter to forward to account(C) and used Run Now button for filter and message sent OK. A few seconds later got message. "Sending of the message failed. An error occurred while sending mail: Outgoing server (SMTP) error. The server responded: timeout (#4.4.2)." This test involved 2 different Output Servers and my 3 accounts. Filter action involved for sure.