Usually, that error message relates to people sending too many messages within a given period of time; a quota has been used up. In these cases as soon as the time period has elapsed the the person is able to send again.

BT Limits: http://btbusiness.custhelp.com/app/answers/detail/c/2048,3433,3434/a_id/18533/kw/size%20limits https://community.bt.com/t5/Email/Email-too-many-recipients/td-p/1036750

re :BT say that as I can send via their website, it must be a client problem. They would only say that if they were lacking in knowledge, had no idea and couldn't be bothered to escalate the issue. Sending via an email client uses POP, IMAP and SMTP, which is not the same as using their webmail server accessed via online website.

If you have not been sending sufficient emails to trigger that message, then it could be..... Someone has been abusing your email address or hacked your account and sent emails. This should be easy for BT to check as they would have a record of loads of emails being sent which you have no knowledge about.

However, it is more likely to be a BT issue. Over the past year there have been many complaints of this nature and it has occurred regardless of what OS and email client.

See bt community forum:

• https://community.bt.com/t5/Email/421-Too-many-messages-1-5-6-1/td-p/1511896
• https://community.bt.com/t5/Email/Error-quot-The-mail-server-responded-Too-many-messages-quot/td-p/1311125

This is a link to the bt service status website. Maybe your area is listed.

• http://btbusiness.custhelp.com/app/service_status#issue36722

I notice that your second image specifically states an IP address. You could try to get your computer/router to use another IP address to see if you get the same result. http://bt.custhelp.com/app/answers/detail/a_id/9609/~/how-do-i-set-my-computer-to-obtain-an-ip-address-from-my-router%2Fhub

I have already seen the threads referred to above, but am pleased that you also think it is more likely to be a BT problem. As far as the IP addresses are concerned, these have varied through the times I have seen the error message. I would have hoped that someone in BT would find the conditions under which the server's response is produced. Someone is due to call me again tomorrow.

My guess is you have legitimately hit this limit at some point, perhaps emailing everyone you had a new email address. What has not happened is the automatic repeal has not occurred as it should.

I have seen the same thing happen on the forum. It limits the number of replies you can make, when I first came here I hit the limit and although the system was supposed to reset the next day it did not and operator involvement was required. Basically you been to get through to level two support at BT where they employ people that do more than read scripts.

Problem now solved. Thanks to the helpful replies (above) and to Apple Support who suggested adding a new email address to my BT account. This worked via webmail and via Thunderbird and Apple Mail, and so convinced me the problem was with my original account and BT rather than any client.

Unfortunately, BT support at Tier 1/Tier 2 kept repeating that they did not support mail clients and so could not do anything, and did not seem to understand the significance of the message returned from the server.

I then contacted BT again, via the "I'm thinking of leaving BT" option. The result was (a) another year's broadband and phone service with a big discount and a Home Hub 5 free of charge; and (b) access to BT Tech Experts (normally chargeable, also free of charge) who eventually discovered the messages counter and reset it. There was no explanation as to why is was set at a value which stopped me send messages, but I'm pleased to be able to send messages again. I will however have to reorganise all my messages, folders and filters as they were mangled during the previous attempts to delete and recreate the accounts on Thunderbird, which was the initial advice from BT.

I may write to the Chairman to express my frustration with their fault process and suggest some improvements.