Your first backup
The first run reads the whole mailbox. The following runs only read what has changed, so the first one is the only long one.
What the first run does
istorel connects to your mail server like a mail client, in read-only mode, and goes through every folder. For each message, it stores two things in two different places.
- The headers go into an index: date, sender, recipients, subject, size, folder. The index is what lets you search a backup without reading the storage.
- The body, with its attachments, is compressed and added to a pack. A pack holds many messages, which keeps the storage cost of a large mailbox down.
How long it takes
It depends on the size of the mailbox and on your mail server. The limit is almost always on the host’s side: how many connections it allows, and how fast it sends the messages.
If a run stops halfway, the work already done is kept. The next run starts where the previous one stopped, and messages already stored are not downloaded again.
The following runs
From the second run on, istorel only asks the server for messages it has not seen yet. IMAP numbers the messages in each folder in a stable way, and istorel records where it stopped.
Some servers reset this numbering, for example after certain migrations. When that happens, istorel reads the folder again from the start. This is rare, and it avoids storing a message under the wrong identity.
What happens to deleted messages
When a message is deleted from the server, it is marked as deleted in the index. Its content stays in the backup, and you can still read and download it.
This is what protects you when someone empties a folder. A copy that also removed deleted messages would only protect you against a disk failure.
If it fails
A failed run shows in Recent runs with its error. By far the most common error is the mail server refusing the credentials, because the application password was changed or revoked at the provider.
After several refusals in a row, the mailbox is suspended so that istorel stops connecting to a server that keeps saying no. Enter the password again to resume it, and the next run picks it up.