Not Receiving Email

Hi,

I have two email accounts with Zoho, one is working and one isn't. The one that isn't receiving (or sending) emails is hello@sketchuphub.com
This started happening at some point last night, as the last email I received was at 11pm. I've checked back office of my WordPress site and a number of emails were sent to the above email address but they weren't displaying in my inbox this morning, then I did two tests. Both emails are in a queue in my sent items, with the error 'Problem communicating with the recipient server'. This is my business email, grateful if you could look into this as soon as possible.

Thanks