Could not sync email and contact.

Could not sync email and contact.

Hi.
I'm having trouble with zoho mail.
Recently, I found that my android phone is no longer syncing with zoho mail and contact.
It's been a while (I saw that my last email was received 3 - 4 weeks earlier, and did not sync anymore since that time), but I did not notice that for a while.
I'm using an android device, through msync.zoho.com, to contact my email account (as written in this message header), hosted by your site.
I have used zoho service (especially my contact) quite a long time (for many years), and it's all gone now, so I'm very embarrassed right now.
Has there any change in your server configuration?
Well I think so because it's worked flawlessly so far, and suddenly stopped working.
I'll be very glad to hear something to fix this situation. thank you very much.

Best regards,
Sungjin, Kim.