I am getting this with iCloud. Any ideas?

I was having this problem for a few days. I realized I was on a secure network at work that was blocking certain connections, so I couldn't use any 3rd party email clients while on the network at work. Perhaps try using a different internet connection and see what happens.

still same aq

Same issue, can't figure it out. I've removed the gmail accounts, still having issues.

4/21/17 IMAP Test Failed. Have a server connection and information is correct. Anybody have any suggestions???

I think I'm moving back to Apple Mail.

I was able to solve this for an icloud account by using an app specific password. Might want to try that and see if it helps.

Same problem on incoming Imap settings on SSL 993, on 143 works good
Hope support team will fix this issue

I had the same issue. Then, after working with the developers we manage to resolved the issue but it worked for a few days before getting errors back again. The developers use to tell me the same thing every time, to delete the account and add it again. But who wants to do this all the time?

GMAIL only but very annoying!

airmail wants money for app buy refueses to issue a fix it seems

I would request you to turn on the option of "Allow less secure apps" in your Yahoo Mail settings.

same problem with yahoo.....

Having the same issue here!

I'm having same problem. I use SMTP2Go for sending of emails. The settings I have work fine on iPad and iPhone and used to work fine in Thunderbird (Thunderbird not supported by Sierra on Mac, hence the switch to AirMail). With it not working using the SMTP2Go setting that work elsewhere I tried to revert back to the outgoing settings I was using briefly (which are those which match my incoming). Now I can't send email at all!

Same here even for gmail

Same here IMAP fail on yahoo - not good enough !!

when can we have an answer on this issue. Strangely enough it worked fine until the end of Feb.

Okay, this is still an issue. Has anyone found a solution? Technical support does not seem to have an answer.

Same here

Same here!