Why Sending is Paused when Using SMTP?
If you're using SMTP as your sending method and sending has been paused, it could be due to a technical issue with SMTP.
When we receive an error from an SMTP server, we evaluate what kind of error it is. If it is a hard error (i.e.: a connection error), we stop sending.
In this case, you need to contact your third party support and ask them for further assistance.
If the error is a soft error, we won't stop the sending because of it. However, it depends on the server and if we are able to detect the error.
If sending is paused when MailPoet encounters an invalid email address (i.e.: an unprocessed subscriber), it means that for some reason SMTP is rejecting these invalid email addresses and returning an error classified as a hard error.
As there is no bounce handling out the box unless you are using our MailPoet Sending Service, you have to delete the subscriber and then resume sending.
You can find out more about bounce management here.
Alternatively, you can contact your host and ask why they are rejecting these specific email addresses or change your sending method.