Mail is not being sent to recipients

Mail is not being sent to recipients

A few emails have been sent today and the recipients are not receiving them. I sent an test email to my personal account from my Zoho account and have not received it. Last email that was successfully received (from Zoho to someone else) was on Feb. 25th. Is there a network issue? I can receive emails (coming into Zoho) just fine.

The mail shows up in the Sent box with no indication of an error and is not in the Retry Mail queue.