The mail server which hosts your mailboxes is rejecting email with the following errors after changing your domain’s MX records in cPanel to point to The Email Laundry servers:
Rejected RCPT: mail.example.com [10.10.10.10] is currently not
permitted to relay through this server. Perhaps you have not logged
into the pop/imap server in the last 30 minutes or do not have SMTP
Authentication turned on in your email client.
The problem lies in the fact that when the domain’s MX records are pointing away from the default ones for the mail server (which is the case when using a 3rd party email filtering service such as The Email Laundry), cPanel believes that it shouldn’t handle email for the domain any more. To solve this issue, cPanel has to be told to accept email for the domain even if the MX records are pointing away from it.
Log into cPanel on one of the domains on your server and click on MX Entries.
Depending on the version of cPanel you are using, there will be different options presented.
Assuming that the domain’s MX records are pointing to The Email Laundry server:
1. If the option ‘Always accept mail locally even if the primary mx does not point to this server’ is present, it should be selected and the settings saved. This will allow the email host to accept email even when the MX records are pointing to The Email Laundry.
2. If there are options under ‘Email Routing’ (cPanel version 11.28+), ‘Local Mail Exchanger’ should be selected. This will allow the email host to accept email even when the MX records are pointing to The Email Laundry.