Subject: We’re sorry about the server outage on [DATE-TIME]
Dear Customer,
Our main server went down at 3AM this morning and it resulted in all your accounts and services being non-functional till 6AM.
We’re truly sorry about what happened and our team of engineers are studying the issue closely to ascertain the reasons for the failure. Please rest assured that we will get to the bottom of it to ensure that it does not happen again. I would also like to assure you that this outage did not result in any loss of data – your accounts should come back just the way you left it.
We appreciate your patience and thank you for your continued support.
Please write back to us if you have any questions.
Sincerely,
[YOUR_NAME]
[YOUR_POSITION]