I'm having the same problem. Another person, who left the organization a year
ago, set up the email accounts.
I have at least 2 generic accounts dumping into mine, and all of a sudden am
prompted to sign in to them, which I normally do not have to do. This has
happened in the past, but then I was able to send & receive mail (but
possibly only using one account?).
Until this morning I had been unable to send or receive email since 4/23.
After I tried Gary's suggestion (Tools/Accounts/Properties/Servers), I can
now receive email, but still my outgoing messages are being held in the Out
Box.