I'm having persistent problems with slow email and dropped connections using IMAP, although I am otherwise able to access the Internet. I use Outlook 2010 as my email client. The slowness means that, when I open Outlook, I have to wait to access my Inbox. Until then Outlook shows "not responding". Sometimes, without warning, I will receive a message that IMAP is unavailable or that I am not connected. The only way to reconnect is to exit and re-enter Outlook. Messages are slow to leave Outbox, too.
Are these known problems with Plusnet/Outlook, and are there any solutions? Would a different email client work better with Plusnet? Any suggestions would be welcome.
It is somewhat difficult to be sure of an answer here, as slow internet connectivity and issues with the mail service (as there are sometimes) will exhibit the same symptoms.
Have you tried looking at your mail box using Webmail? If there is an email with a large attachment waiting to down load, you might well see the symptoms you describe.
There are known intermittent operational issues with IMAP / webmail, which are made worse with large mailboxes.
I use OL 2016 largely without issue, though sometimes it can be sluggish and connections fail. It is not entirely clear if this is a connection or a responsiveness issue, for I also occasionally see web page retrieval requests fail which work on a refresh.