Most of my emails get through to the recipients, but several intended recipients recently have told me they have not received my emails. When I check the sendmail log for each of these, I see:
"stat=deferred" (usually followed by "connection reset by...")
Looking further at the log, there are a variety of "stat=deferred" messages with various messages like "operation timed out", "greylisting in action", "please try again later", etc. (I can't tell whether most of these were received or not).
Do I have a problem at my end, or is it an issue with the recipients?