The retry timeout setting defines how often the MTA (Mail Transfer Agent) will try to deliver messages that cannot be delivered at the first attempt.
Eltris's servers use Exim for Mail Transfer Agent and Postmark for email delivery. If an email cannot be delivered at the first attempt, Postmark tries to resend the message every 15 minutes for 2 hours. Then the retry intervals are increased, starting at 1 hour and increasing each time by a factor of 1.5, up to 16 hours. Then Postmark retries every 8 hours until 4 days have passed since the first failed delivery.
If the message delivery fails, you will receive a bounce-back email explaining the reason why the delivery failed.
This is the default setting on our servers. It cannot be changed on the shared servers due to their specific setup and security policy.