The question was about Zoho, but I'll respond about the other two:
- bk.ru is Mail.ru
When they added IMAP in 2011 or 2012, they did not implement server search.
"Promised" to do it "soon", it's 2016 now, still has not happened.
Has to be fixed by Mail.ru but won't be.
Not related to Zoho.
- outlook.com
As you and I already discussed a couple of weeks ago, this is broken on those "new servers" since the upgrade.
I believe only searching for "sender" or "headers" is affected -- while searching for "full text" still works.
Has to be fixed by MS and might be.
Not related to Zoho.
- Zoho
Got your log.
Yes, server issue.
They're unable to handle the search command variation which is used when searching for "sender" or "headers" (which is what's in your log).
Searching for "full text" should probably work, haven't heard otherwise from other users, but you log has only has sender/headers search.
Has to be fixed by Zoho, no predictions.
Sending: kman34 SEARCH RETURN (ALL) CHARSET US-ASCII OR FROM {16}
Got: kman34 BAD syntax: expecting 'c', found 'h'

What the heck is this "expecting c found h"?