Email forwarder seems to work sometimes

What is the name of the domain?

mcmullanfamily.org.uk

What is the error number?

521 5.3.0

What is the error message?

host route1.mx.cloudflare.net[162.159.205.12] said: 521 5.3.0 Upstream error

What is the issue you’re encountering

Email forwarding does not work

What steps have you taken to resolve the issue?

Periodically sending myself emails to see if it works

What are the steps to reproduce the issue?

Send an email to [email protected]
One person has managed to send an email to [email protected] No others seem to have got through, though. According to my dashboard, of 30 received, 14 have been forwarded.
I’ve received one.
Pease help.

A post was merged into an existing topic: Email forwarder responds with “Undelivered Mail Returned to sender”