i use thunderbird-problem :i can receive email but cannot send.

For anyone to assist you, we need to see the actual error message and a screenshot of your SMTP server settings pane. thank you

I'm submitting how I solved my problem. I had that same problem. My error said that the incoming and outgoing smtp need to be the same. I use Spectrum but I have been using their "old format" of RoadRunner for almost 20 years. I use pop server, not IMAP. So, for me, the solution was making sure the outgoing smtp was the same as incoming...pop-server.wi.rr.com. Maybe this may help...good luck.