not the server?

Effectively, NO e-mail address can contain any comma.
If there is a comma in place of a dot, it was probably substituted by accident as they are next to each other and can look similar if you are not attentive.

Locate the incorrect address and open it's properties. From there, you should be able to edit any field. Replace the comma by a dot, or maybe you just need to remove it.

Save your changes.

Electro
June 2012