All email message with x.x.x format like 4.3.4 originate from mail servers. So if your mail provider is shaw, then shaw's mail server is responding refusing to send the mail because you have in it's opinion exceeded the allocated resources. I am guessing that you have probably sent to many email in a 24 hour period, but that is something of a guess. You would need to ask shaw why their mail server is telling you that..

I have never heard of Shaw.... My provider is Century Link. I also only sent 5 emails out yesterday. I don't have any restrictions on how many I can send either. I have never had an email problem like this before and have had it since 1992. Just weird..

Matt's advice stands, in principle; ask the Century Link helpdesk what the error message means. It is from a server, not from Thunderbird itself.

It could just mean it's too busy and overloaded and they need to be told so they can think about upgrading their system.

OK, thank you zenos...

I suspected it might have something to do with them, getting thru will be a challenge.  Happy to hear it has nothing to do with Thunderbird.

I had this problem and fixed it. Centurylink does not actually delete messages at the behest of Thunderbird. So although on Thunderbird it looks like you have cleaned out old mail, or moved it to local folders, the old mail actually continues to accumulate on your Centurylink account until it fills up your quota. That's when these "allocated resources exceeded" messages start up. The temporary solution is to login to Centurylink web mail and go through all of your mail folders there, deleting old mail that you thought was already deleted. That will likely fix the problem for at least a number of months, until you fill your quota of disk space up again.

You can avoid accumulating messages on your mail server by changing your Thunderbird settings. Doing so, however, will cause your messages to be downloaded onto whichever device you are currently using to read email. Those messages will then only be available there. This can be confusing if you read mail using multiple devices (i.e.: cell phone and laptop).

If you want to make this change, click on the account name in Thunderbird, and click on View settings for this account. Then select Server Settings. Uncheck "Leave messages on server". Them click on Ok.

Yeah, OK, if this account uses POP. I don't think the OP has told us this.

If it's happening with IMAP you won't have that particular checkbox; your only recourse then is to move older messages out of the account and into Local Folders, or export them to regular files accessible to your file manager.

Here's what I stumbled onto by accident (I'm retired so no longer need to fake expertise):

When I get the 4.3.4 error I leave TB open, then I sign into go to the CenturyLink webmail from my browser and return to TB and send emails with no more 4.3.4 errors.

Note: The Century Link support people don't seem to be problem solvers. It's easier to say, "We don't support TB." even when it's their problem.

StoryGordon said

Here's what I stumbled onto by accident (I'm retired so no longer need to fake expertise): When I get the 4.3.4 error I leave TB open, then I sign into go to the CenturyLink webmail from my browser and return to TB and send emails with no more 4.3.4 errors. Note: The Century Link support people don't seem to be problem solvers. It's easier to say, "We don't support TB." even when it's their problem.

Try this. Get mail from century link immediately before you click send. Some ancient email configurations used a get before send authentication method that may be at work here.

Thanks, Matt,

the 4.3.4 error occurs only occasionally. I'll try "Get Messages" then "Send" next time. Much easier than going to webmail.

I am going to try Matt's latest suggestion of getting mail, then sending. Its counter productive to have to log into CL, just to make something work that should work without doing that. If I had to do that I would use their mail instead of what I like... As for all the other suggestions that I marked as not solved. I have already done most of everything suggested. I have no mail accumulating on webmail for CL and no mail in their folders either. I don't get or send excessive mails so there is no limit and never did. My mail comes into Thunderbird without a copy left on CL. I do have a POP for Thunderbird, I also use 995 and 587. Last night I tried 6 times to send and finally used my gmail account instead. Thunderbird should work now for a few days maybe a week, so I am going to try to do the "get mail first", from now on and see what happens. I am also going to call CL and see if I can get some sort of "knowledgeable" person to address this problem if at all since, ( in my case ), it has only started since they changed the 'look' of their email app to upgrade it. I guess they are trying to get more users.

But like I said before, I am a retired old lady and they refuse to listen to comments from someone who isn't an actual 'tech' person. In 25 years of having emails and the last 10 thru CL for my server this has never happened before.

Many thanks to all the suggestions from all of you.

Me, too. While it's counter productive to log into CL, it works which is better than not being able to send messages knowing Matt's solution.

It's coming and going again. Gone for now. I'll use webmail when it's broken.