Some providers require you to use their internet service to send mail. Comcast used to be a big player that did that. So folks would go on a cruise or the like and be unable to send mail for the duration. So the first thing to look at is the server name you are sending from and checking with your provider if that is the one you should use for "mobile" devices. As I don't see any mention of the email providers name anywhere in your many posts that I looked at. That is about all anyone can tell you.

Why are you not sending using mobile data? Does it work if you do? I looked at your other questions in the hope of learning anything useful about your mail provider or setup. Many posts. No useful information supplied at all. Either relevant to this post, or any of the others, you do not provide any information to those that might support you those in the forums know exactly what you tell them. So even if there is a well known issue with say Google and they are you provider, you will hear crickets as a response because no one has any knowledge that it is relevant to you.

It is even possible this is relevant here https://support.mozilla.org/en-US/kb/thunderbird-smtp-ehlo anything that is advertised as protecting privacy causes issue with some providers. It is almost a given. That is the same to some servers as using a VPN. I might hazard a guess Google will take it badly as they use reverse DNS to check you are where you say your are.

But I do not support the Android product. Hopefully somebody will reply to you in the Android forum if you supply enough inforamtion.

Like I said, using exactly the same settings (Zen Internet), I can send from home no problem. I'm not using mobile data, the obvious solution, because it doesn't sort out why Thunderbird can't send when other email apps can. I've had this posted in Android with no reply for about a week, which seems normal there. There also doesn't seem to be any way to get to Mozilla Support, if that exists. Nothing useful comes up on a Google search. That's why I tried here as a last resort.

Hi

This is the Mozilla Support forum for Thunderbird for Android.

When you are away from home, are you using WiFi or mobile data?

WiFi - that's why I said when connected to the Internet. I always use WiFi - it works at home, but, with exactly the same settings, does not work away from home. It's nothing to do with a VPN and is only a problem with Thunderbird, not Gmail, Proton Mail or Outlook. Am I really the only person with this problem?

Edit 20 May I have just tested sending by mobile data (Wi-Fi turned off). both in a cafe and at home, and Thunderbird for Android fails to send on either, while Gmail and Proton Mail do. Am now even more confused

Latest edit

Using Thunderbird for Android from home - Using Wifi, going into server settings for Thunderbird and clicking on Verify, they get verified. Turning off WIFI and using mobile data, I do exactly the same and get SmtpResponseParser -exception Unexpected end of stream