Perhaps not the cause, but isitdownrightnow.com is showing that both IMAP servers for ZOHO are down. If that's correct, then this isn't an AM problem and there's nothing that can be done from the AM side.
What is the specific URL that shows Zoho IMAP servers are down (and where/region)?
I provided the URL to Is It Down Right Now. Follow the link and then enter the server address you're trying to use. I used imap.zoho.com and imappro.zoho.com. Both showed as down. And again this morning. Although I do admit it's interesting that you're able to connect via other apps. I guess you're just going to have to wait for Kostya to weigh in on the issue.
Ah, okay I see. I don't think that service is capable of checking anything other than HTTP port 80 URLs. For example, if you enter
imap.gmail.com it will redirect to checking
mail.google.com/mail/ (and pass). That one seems hard coded into the site. If, for example, you similarly try
imap.zoho.com or
imap.mail.yahoo.com, they don't redirect to anything else and fail, but not because they are down (they are, in fact, up); but because that service only supports HTTP port 80 services, which IMAP isn't. To be honest, I always use
telnet(1M) for these matters, and this is what it has to say (from my UNIX prompt):
user@fedoraLinux$ telnet imap.gmail.com 993
Trying 173.194.207.109...
Connected to imap.gmail.com.
Escape character is '^]'. <---------- Connected successfully and waiting for me.
^C
Connection closed by foreign host.
user@fedoraLinux$
user@fedoraLinux$ telnet imap.zoho.com 993
Trying 204.141.43.211...
Connected to imap.zoho.com.
Escape character is '^]'. <---------- Connected successfully and waiting for me.
^C
Connection closed by foreign host.
user@fedoraLinux$
user@fedoraLinux$ telnet imappro.zoho.com 993
Trying 204.141.43.212...
Connected to imappro.zoho.com.
Escape character is '^]'. <---------- Connected successfully and waiting for me.
^C
Connection closed by foreign host.
user@fedoraLinux
user@fedoraLinux$ telnet imap.zoho.com 994 <---- Intentionally use the wrong port (not 993)
Trying 204.141.43.211...
^C <-------- Hangs forever, or until Ctrl-C or telnet client timeout. This is the correct behavior.
user@fedoraLinux$
So both Zoho IMAP servers have been up. telnet(1M) says so, and even better, so does the GMAIL Android client (which does an even deeper inspection by connecting via SSL and authenticating).