The Fox Feed

The solution is to reduce the maximum number of connections in Thunderbird. This can be done from

Edit > Account Settings > Server Settings (for the account) > Advanced > Maximum Number of server connections to cache.

Referance:

• https://www.siteground.com/kb/you_may_have_exceeded_the_maximum_number_of_connections/
• https://www.electrictoolbox.com/thunderbird-exceeded-maximum-connections-imap-server/
• https://bugzilla.mozilla.org/show_bug.cgi?id=561055