When people outside of your organization send you email, their email systems don't double-check where to send that email ...

When people outside of your organization send you email, their email systems don't double-check where to send that email every time. Instead, their systems save the location of your email system based on a setting in your DNS server known as a time-to-live (TTL). If you change the location of your email system before the TTL expires, the sender's email system tries to send the email to the old location before determining that the location has changed. This can result in a mail delivery delay. One way to avoid this is to lower the TTL that your DNS server gives to servers outside of your organization. This will make the other organizations refresh the location of your email system more often.