The SMTP protocol has always supported servers temporarily down. The nominal use case is that a message is sent by an email user agent (usually a mail reader like Thunderbird) to its nearest mail transfer agent (sendmail, postfix). , exim, etc.), which is declared as the SMTP server.
Then, the MTA attempts to deliver the message to a recipient. sender it lacks connectivity (common to the corporate network) or an SMTP server that states that it can process the recipient's e-mail address. One or more relay can be involved in the chain.
And each MTA agent in the chain is normally able to queue the message for a variable length of time (usually between a few hours and a few days) until its next hop is respected.
The only problem is that there is no tool to find out where a mail can be queued up. The only way I know is to contact the administrator of the first SMTP host and ask him if the mail is still in his queue or has been delivered and where, and repeat the chain up to that you find the mail or that you can not get an answer. admins.
In short, if you know the senders, the only reliable way to ask them to send the mail to a different address. If you do not do it and the email provider can not get it back in a short time, I can not imagine any solution.