Could it be outgoing.verizon.net? Verizon DSL is my ISP. I have linked Yahoo with Verizon. I use Yahoo for sending and receiving email. I have different email addresses for Verizon and Yahoo, but only use Verizon email address for my billing info, sub accounts and account switching. If I'm not in Yahoo to send an email, Mac Mail automatically pops up. Mac Mail is constantly rejecting passwords, mail server is never correct. I am very confused about this. I have battled this same problem for several years.