Mail.app has no entry for from: gmail-account I'm using OSX10.11.4. I've got several mail accounts and use mail.app to receive and send mails. One of these accounts is a gmail Account. I'm able to receive all mails with mail.app but I can't send a mail from my gmail Account. 

With all other accounts it's possible to receive and send, gmail is the only one where I'm only able to receive but not to send mails. If I want to send a mail the gmail account is not listed at the from dropdown-field.

I used default settings to set up the account at mail.app and does not change something. 

Hope someone has an idea.
You could just go into Mail/Preferences/Outgoing Mail settings and verify the SMTP settings. 
Gmail uses smtp.gmail.com on port 465