Mail shows my SMTP is "offline": How do I get my SMTP "online"?

Thank you so much - it was touch and go between tears and tantrums...

Great fix.

This worked for me , sign in to your google account ,go to sign in & security, turn on allow less secure apps to on . not an apple problem lies with microsoft !

There was already some information under DNS servers. If I would have just added those servers the others would have disappeared. I wrote them down, entered the DNS servers you suggested, then entered the previously-existing info after. Immediately, Mail started working again! Thank you for sharing.

I'm not sure how relevant this solution is to the original issue, but I'll offer it to the community for what it's worth. I've experienced several occasional SMTP Offline conditions that I could not resolve or was unwilling to try the solutions offered in this support community. Mostly because I didn't understand what the replies were telling me to do. At some point they start to sound like Windows garble. Regardless, my issue appears to be connected to my iPhone and iPad that I use for work (through our Outlook server) and occasionally change to my personal (Comcast/Apple) account to check my personal emails. Each time I switched my iPad to my personal account my iMac STMP switches Offline. When I switch back to my work account the iMac STMP switches back Online.

Hope this helps.

Thank you! This worked for me...

Thank you so much for this. I have been trying to fix my Comcast email for a long time and now it works!

This works the same with Yahoo. Thank you for posting.

I am still not able to get it to work. I'm running OS X 10.12.1, and Mac Mail 10.1. I have two gmail accounts, one at gmail.com, the other through my university.edu. In both cases, my Mac Mail program is showing the IMAP connection to be fine, but the SMTP to be offline. I tried deleted both through System Preferences > Internet Accounts, and reading them. I made sure "Access for Less Secure Apps" was turned ON for both accounts. Still no connection. Then I went to Mail > Preferences > Accounts > Server Settings > Outgoing Mail Account > Edit SMTP List, and this is where it got a little weird. Though in Outgoing Mail Account I could select from three different possible servers (for each of my three emails), when I went to Edit SMTP List the list was totally blank. Nothing on it at all. I tried to add a new one using these settings (https://support.google.com/a/answer/176600?hl=en) but it isn't selecting, is weirdly disappearing from the list, and regardless isn't connecting at all. I am not sure what to do. Any suggestions?

You might want to consider starting a new discussion. Since this one is a couple of years old, less people are likely to look at it. A new post would be much more visible. You can link to this one. Post in the Sierra community.

This worked well for me. Thank you