Email - Forwarding not working

I have a client that has an email address that is set to forward mail to a yahoo and to an aol account. He is seeing mail be forwarded to the aol account, but the yahoo account is receiving nothing.

This has always worked and he just started noticing it today. I am having him try and send directly from his account via web mail to see if it is something specific with the mail server versus the forwarding settings.

His settings in the panel for the mail server is mail2 → mail4.

Anyone else experience any issues like this?

We also went to web mail and tried to email several yahoo accounts and nothing. This was coming from mail4.

We used a different email address from my account which is mail3 and it will go through… so it seems isolated to mail3.

[EDIT] I mean isolated to mail4.