Ok, I just turned off my VPN and can now receive mails form all accounts, but sending still not working.

Do you have separate smtp servers for each account, and is each account sending on a matching smtp (not all sending on a Default smtp)?

https://support.mozilla.org/en-US/questions/1350593

Thank you sfhowes I actually do have differrent smtp servers set up, one for each provider. You may not believe this, but today I can suddenly send mail from my main account at posteo. However, when I try to send mail from any of the other accounts I get another error, sigh...

Besides having different smtp servers, confirm that each account is sending on the correct smtp (select the account in the left pane of Account Settings, then check Outgoing Server (SMTP) in the right pane).

Check that smtp settings for gmail are smtp.gmail.com, 465, SSL/TLS, OAuth2, and smtp.mail.yahoo.com, 465, SSL/TLS, OAuth2.

I can't read the German error, but it suggests you have some kind of spam protection working only for the posteo account - which shouldn't be a factor unless the gmail or yahoo accounts are mistakenly trying to send through the posteo smtp.

again, my thanks sfhowes, that did the trick!

Unfortunately, I still do not receive anything from Washington Post emails. Can you tell me what is being done, or how I can fix this situation? I have a paid subscription for all-access digital. thanks, Carol Krueger [email]@comcast.net