emails stuck in outbox

[e8vww]

Sometimes when I use Send Later the emails end up unsent, stuck in the local outbox.

I tried searching the help articles but found no results for this specific problem. Thanks for your help.

thunderbird 91.6.1, send later 9.0.9

[jph-sendlater]

Does File > Send Unsent Messages work to manually send the messages from the outbox?