Hello everyone! I have a question to ask. We have two mx records, mx1.domain.com and mx2.domain.com, with priority values of 10 and 20 respectively. Both servers are currently available. However, there is a difference between them: while there is a mailbox (user444@domain.com) on mx2 (which has a lower priority value), there is none on mx1 (which has the higher priority value). Therefore, if a letter is sent to user444@domain.com, it will be delivered to mx2 first. Only if the mailbox is not found will the letter then be sent to mx1. If the mailbox still cannot be located, a bounce message indicating that it does not exist will be returned.

On a related note, it's always important to ensure that your mail server settings are properly configured to avoid such issues.

There are several solutions to the issue at hand:
- Disconnect the server from mx1 so that all email goes to mx2.
- Swap the priorities of the MX records, but this could potentially result in mail not being delivered if the first server is unavailable for any reason.
- Create a mailbox on the server with mx1.
- Ensure that all mailboxes are located on one server, with the second server acting as a backup. The backup server should not have any mailboxes, but must be configured to receive all mail from the domain. The main server should retrieve mail from the backup server in the event of failures or power outages.
- Configure multipop on the mx1 server to collect mail from mx2 for any mailbox, including user444@domain.com.
- Configure and raise the server as a mail gateway without its own mailboxes. It should accept domain mail and forward it to your servers.

It's important to note that when migrating to a new setup, creating a common address space should be a primary consideration. While it may be possible to do so with your own servers, it may not work with Google. In the case of Google, you would need to configure forwarding of email from postfix to the appropriate Google boxes via a transport map. However, there is a risk that Google will flag these forwarded emails as forged and discard them.

An MX record is a text record that provides information about mail servers responsible for handling email. If the MX record on the recipient's side is configured incorrectly or nonexistent, they will not receive emails directed at them. To configure the MX record, you should access the website of your domain provider, log in to your personal account, navigate to the domain management section and add an entry accordingly.

There are two methods for checking if the MX record is configured properly: through an online service or through the command line on a desktop. It's worth noting that ensuring proper configuration of the MX record is crucial for successful email delivery.

In your scenario, you have two MX records set up: mx1.domain.com with a priority of 10 and mx2.domain.com with a priority of 20. This priority system dictates how emails are routed when sent to user444@domain.com. The lower the priority number, the higher the priority of the mail server. Thus, in optimal conditions, mx1 should handle the incoming mail first.

However, since there is an existing mailbox at mx2 but none at mx1, this leads to an interesting situation. When an email is sent to user444@domain.com, the mail transfer agent (MTA) first directs the email to mx2 due to its current configuration. Since a mailbox exists there, the email will be delivered successfully to user444@domain.com.

If for any reason the mailbox at mx2 was unavailable, or if mx2 were to be taken down, the MTA would then attempt delivery to mx1. Since there is no mailbox for user444 at mx1, the mail server would send back a bounce message indicating that the recipient does not exist.

This setup highlights an important aspect of email server configuration: the presence of mailboxes on the servers designated as MX hosts. To avoid possible delivery issues, it's crucial to ensure that all high-priority MX records have active mailboxes configured.

Additionally, if you anticipate that mx1 could have heavier usage or need redundancy, I would recommend creating a similar mailbox for user444@domain.com on mx1. This way, even if mx2 fails or becomes unreachable, mx1 can still take over the delivery without resulting in bounce messages, thus maintaining communication reliability.

It's also worth noting that proper monitoring and alerts for your MX servers can catch these potential issues early. Ensuring backups and redundancy can protect against the loss of communication, which is vital for any business relying on email for operational purposes.