[X4U] Unable to send mail

[Richard H Stoddard]

I am suddenly unable to send emails.  My default mail app is GyazMail, and tonight I get the following error message whenever I try to send a message:

"SMTP Protocol Error: 554 5.7.1 Service Unavailable for sergio52 at mac.com - Please disinfect your computer. [slot 2]"

I have no idea who this sergio52 at mac.com is. Using Mail.app, I just get the message that it was unable to connect to the smtp server.

I did a virus scan over the weekend, so would be surprised if in fact my system is infected.  Has anyone seen such an error message or have any idea what's happening?

Thanks,
Rick