Bugzilla

While doing some testing for bug 1955589, I encountered the following error from the Exchange server we're testing against:

```
[ERROR ews_xpcom::client] an error occurred while attempting to copy the message: ResponseError { code: ErrorMailboxStoreUnavailable, message: Some("The mailbox database is temporarily unavailable., Cannot open mailbox. Server = SA1PR05MB7919.namprd05.prod.outlook.com, mdbGuid = 4e558c61-9aa7-400f-9023-edd9c893b345, maiboxGuid = bb0f9083-1bfa-4ee3-8851-876b23ed0046") }
```

Repeating the operation worked, which confirms this is a temporary issue. When something like this happens, we should trigger the retry logic that already exists to handle rate limits (implemented in bug 1892085), with some arbitrary value for the sleep timer.

While doing some testing for bug 1955589, I encountered the following error from the Exchange server we're testing against:

```
[ERROR ews_xpcom::client] an error occurred while attempting to copy the message: ResponseError { code: ErrorMailboxStoreUnavailable, message: Some("The mailbox database is temporarily unavailable., Cannot open mailbox. Server = SA1PR05MB7919.namprd05.prod.outlook.com, mdbGuid = 4e558c61-9aa7-400f-9023-edd9c893b345, maiboxGuid = bb0f9083-1bfa-4ee3-8851-876b23ed0046") }
```

Repeating the operation worked without any error, which confirms this is a temporary issue coming from the Exchange backend. When something like this happens, we should trigger the retry logic that already exists to handle rate limits (implemented in bug 1892085), with some arbitrary value for the sleep timer.