Sounds to me like whatever is in your signature is being recognized by those services as SPAM or Malware. Did you perchance create this professional signature in Word?

Hello Matt,

thanks for answering. I researched how to put it in HTML, and spent hours on that (under account settings, signature text). It was working for a while, but today all emails with a signature aren't being received. Even after taking it out of html, and pasting the signature on the email, it doesn't go through.

There is a reason we suggest only composing HTML signature in the composer and saving the file. However, could you email me to see what that signature actually looks like (It might bounce we will see how google likes it.) this forum really messes up HTML source

Click on my name beside the response on the forum for my email address.