Repeated server connection issues

Hi there I have been using Thunderbird for many years to manage the same many mail accounts on diverse PCs. I prefer using a portable version from portableapps.com, partly because when it comes to transferring to another gadget, it suffices just moving the portable folder, and I do not have to create dozens of accounts in a fresh install. Of late, I have been getting frequent irritating error messages for 2 Yahoo accounts. It connects to them & I can receive mail, but for automatic connections to the server in between, I keep getting error messages like: ''The current operation on 'inbox' did not succeed.' The mail account to abc@yahoo.com responded: p.', ... etc The other day, after reading about possible solutions from some forums, I decided to just delete both accounts and used the recommended Thunderbird connection settings for Yahoo to create the 2 accounts anew. I thought the problem was solved, only to have the same alerts every now & then reappearing, which amounts to a lot, if you have Thunderbird on many hours a day. I consistently update Thunderbird, the moment I'm alerted to a new version. I also have Gmail, Outlook, AOL(AIM) & other accounts, but not get similar issues. How do I permanently solve this problem? Thank you in advance.