Zoho Mail Issues (cannot send, slowness in file attachments, cannot connect to server)

Zoho Mail Issues (cannot send, slowness in file attachments, cannot connect to server)

Our team is currently experiencing the following issues in Mail.

1. Cannot sent mail
2. slow in attaching files
3. cannot connect to the messaging server
4. blank screen

No issues with our current ISP as tracert results are okay.  

Can you assist ASAP?