User Migration Tool, not working

Problem reported by Paul White - 9/16/2026 at 6:41 AM

Submitted

I have client with 10 users that was formally hosting with google workspace (gmail) for their domain. I am in the process of migrating them to my SmarterMail server where hosting will cost much less. Each user has about 40GB of email. I have already setup the domain and the 10 years within smartermail. I have not pointed the DNS yet. Using the built in MIgration tool I am in the process of migrating all their data to smartermail, but the migration fails for some users for unknown reasons. I did check the IMAP retrival logs and it does show Google timing out the IMAP connections after a few minutes.

Smartermail trys to grab lets say 80 emails from a folder. It is able to get a limited number of them, before gmail times out the IMAP connection. Then it waits and trys again later picking up where it left off.

Of the 6 users I started the migration process only one seems to still be moving data. The other 5 stopped. Here are the logs for one of them. This user has 40GB of data, the first time only 13 GB were moved before it failed. I restarted the migration a second time and only 4.22GB were transferred.

[2026.09.16] 00:48:44.257 [882] [user@domain.com; imap.gmail.com:user@domain.com] Skipping email [2]; Folder: Job 811_; Size: 6381556 bytes; UID: 4

[2026.09.16] 00:48:44.258 [882] [user@domain.com; imap.gmail.com:user@domain.com] Downloaded 3 messages from folder "Job 811_"

[2026.09.16] 00:48:44.258 [882] [user@domain.com; imap.gmail.com:user@domain.com] Downloading messages from folder "Job 811_" failed. Re-trying ...

[2026.09.16] 00:49:25.239 [882] [user@domain.com; imap.gmail.com:user@domain.com] Index was outside the bounds of the array.

[2026.09.16] at SmarterMail.MailService.RelayServer.Clients.IMAP.丅丝.AuthenticatePlain(IImapAccountV1Readonly account)

[2026.09.16] at SmarterMail.MailService.RelayServer.MessageRetrieval.丄俌.DownloadMessages(丄俙 trackingFile)

[2026.09.16] 00:49:25.240 [882] [user@domain.com; imap.gmail.com:user@domain.com] Mailbox Migration failed for user@domain.com

[2026.09.16] 00:49:25.241 [882] [user@domain.com; imap.gmail.com:user@domain.com] Processing completed.

[2026.09.16] 00:49:25.246 [882] [user@domain.com; imap.gmail.com:user@domain.com] Sent migration summary message

[2026.09.16] 00:49:25.247 [882] Finished processing for user@domain.com [d67da20e500a4ef9a885e189a54aba86]

Any thoughts on what the problem could be and how to resolve this?

5 Replies

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Andrew Barker Replied

9/16/2026 at 7:13 AM

Employee Post

The first line in that log snippet should only be added to the log immediately after an exception. Without that exception, there isn't really any way for us to say why the message was skipped.

As for the exception that is in the log lines you provided, it looks like there was some sort of issue when trying to authenticate the connection on a retry. That should only happen if the connection is dropped right in the middle of the authentication process. That could be due to security hardware that monitors your outbound connections or because Gmail's servers dropped the connection for some reason.

Andrew Barker
Lead Software Developer
SmarterTools Inc.
www.smartertools.com

Paul White Replied

9/16/2026 at 8:29 AM

I get its running into timeouts from google's side, but shouldn't smartermail retry over and over? Does Smartermail give up after so many retries? This is causing issues as smartermail gives up with less than half the emails migrated

Andrew Barker Replied

9/16/2026 at 11:52 AM

Employee Post

It depends on when the error occurs. If the error occurs during authentication, the migration will not retry. If an exception occurs while downloading messages from a specific folder, the migration will retry downloading messages from that folder. If a second exception occurs on that folder, the migration will pause for 10 seconds then try again. If any more exceptions occur on that folder, the folder will be skipped and the migration will continue with other folders.

If you want SmarterMail to keep trying, you may be better off configuring message retrieval for the accounts. The main difference between message retrieval and migration is that the migration is a one-time attempt. Once an attempt is completed, the migration configuration is deleted from the account. With message retrieval, it can later be re-run - either manually or automatically - and it will get anything that is new since the last time it ran, which is an additional benefit if the MX records are still pointing at the Google Workspace service since.

Andrew Barker
Lead Software Developer
SmarterTools Inc.
www.smartertools.com

Paul White Replied

9/16/2026 at 1:36 PM

Andrew thanks for the suggestion on message retrieval. I will give that a shot. Just to be clear will that check all folders and subfolders, and download any missing emails without creating duplicates correct?

Andrew Barker Replied

9/16/2026 at 1:59 PM

Employee Post

Yes, message retrieval will check all folders and subfolders.

As for the possibility of duplicates, if messages have already been imported to the account using migration, the new message retrieval configuration will not be aware of that. If you switch from migration to message retrieval on an account, I recommend deleting out the previously migrated messages first to avoid duplicates. Once the retrieval is running, it should not pull any duplicate messages.

Andrew Barker
Lead Software Developer
SmarterTools Inc.
www.smartertools.com

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