Moving this from a downstream bug report:
https://bugzilla.redhat.com/show_bug.cgi?id=663738



evolution-2.32.1-1.fc14.x86_64

Apparently some time 3 days ago I sent an e-mail which was rejected by my local
smtp server because the RCPT was unknown (typo in the address).  I do not
remember having seen an error message, but it's possible.  I noticed today that
my e-mail was not sending, it was just backing up in the outbox.  I clicked
send/receive and got not error pop-ups nor errors in the bottom bar.  E-mails
just sat in the outbox.  I stopped evolution and started it again.  No errors
on start up.  I clicked send/receive and this time I got a pop-up error about a
message being rejected by the local smtp server due to unknown user.  I deleted
that message from my outbox and hit send/receive.  This time I got a popup
error saying something like "Failed to append to: unknown error   appending to
local sent folder instead"  (I'm not certain that exactly correct, but I know
the "unknown error" part is right)    But, the top message in the outbox went
out.  I clicked send/receive again, got the same popup, and the new top message
went out.  So at least I could send one at a time....    I went into
edit->preferences->mail accounts->edit->defaults and changed the "Sent Messages
Folder" from "<click there to select a folder>" to a folder on the server.  I
click send/receive and they all went out!

So numerous problems..

1) no error message on send/recv if the local smtp server rejects the message
due to RCPT unknown on the second try.
2) if non-fatal error encountered will not continue to send other messages in
outbox
3) not having a folder set in "Sent Messages Folder" is a non-fatal error
4) no error message on startup about failure to send things in outbox at all

Basically if there is any chance and e-mail can go out, I want it to go out,
not just sit there silently...   I've wondered why people have been ignoring my
contributions to conversations for days....

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With respect of 4), there was a bug that Evolution wasn't trying to flush Outbox on start, which is fixed in 2.91.4.