All other accounts (Gmail, Yahoo, Hotmail/Live) work in Tbird with avast! inbound scan enabled; only Verizon is affected.
I’ve tried the various expert settings in the mail shield, including adding incoming.yahoo.verizon.net to the SSL account list @ no encryption. I’ve tried various settings in Tbird as well.
The only way to login to my Verizon accounts in Tbird is by disabling avast! inbound message scan.
Suggestions? Something I’m overlooking or just an issue with avast?
Welcome to the forums, Arrr! 
I can not be of much assistance since I only use the safest email available … web based email.
But there are many others here who download email into a program on their computers & should be able to help you. Hopefully, someone will post help for you soon.
And now it’s blocking gmail smtp out. >:(
Have you checked out this for your settings: http://support.avast.com/index.php?_m=knowledgebase&_a=viewarticle&kbarticleid=458
I had avast! and Tbird (Gmail) set for TLS on port 587.
Tbird (Gmail) smtp is now working with avast! as SSL on port 465.
It’s odd that avast! would block TLS, since that option exists in the SSL accounts menu.
Verizon smtp (Tbird) also works when set as SSL on port 465.
However, nothing I’ve tried makes avast! allow Verizon incoming.