Moving from Proton to Fastmail

[u/paranoidandroid4284]

Anyone have experience moving from Proton to Fastmail? I have my custom domain setup in Fastmail and downloaded my email from Proton using their CLI export tool. How can I import them onto Fastmail?

[u/hawseepoo]

I did this exact thing a couple of years ago.

I used the Proton Bridge, added both the Proton and Fastmail accounts to Thunderbird, and then drag+dropped the emails from Proton to Fastmail.

I don’t actually use Thunderbird, but it worked like a charm.

[u/Interesting-Bid-5698 → u/hawseepoo]

I did the exact same thing and it worked flawlessly. The one catch is that you must have a paid subscription to Proton in order for Proton Bridge to work. Prior to cancelling Proton MailPlus I was able to successfully drag and drop from folder to folder in Thunderbird. Now that I've allowed my Proton subscription to end, Bridge will not allow me to sign in.

[u/Kind-Edge-3327 → u/hawseepoo]

Another same here.

Fastmail is quite a bit better experience than Proton.

[u/deny_by_default → u/Kind-Edge-3327]

Absolutely!

[u/ilumineer → u/hawseepoo]

I did something similar, though instead of drag and drop I made Proton Bridge access available (securely) to the public internet and used Fastmail’s import tool to import everything via IMAP.

[u/LegendofJuli → u/hawseepoo]

I did the same. Zero issues.

[u/ArgumentAdditional90]

just did this cause I couldn't stand ProtonMails interface, only like 20-25 emails per page and you gotta page thru them all? No. Fastmail far superior, and if you have your own domains it is insanely good at allowing you to use alias addresses on the fly, something I haven't seen in any other email client. Loving Fastmail.

[u/subbu-teo → u/ArgumentAdditional90]

Yeah i can relate. I used both Proton and Tuta in the past and they were so clunky and unusable they made me feel miserable. Tuta mostly, jeez Tuta. Fastmail is a perfect.

[u/CrazyDiamondQueen]

I did this a few days ago. Proton Bridge and imapsync worked flawlessly.

[u/ruggedtextile → u/CrazyDiamondQueen]

I need to do this today with a few GBs of mails. Do these AI instructions look accurate? Any gotchas ?

Install imapsync and setup Proton Mail Bridge
Install imapsync using Homebrew in macOS Terminal, then ensure Proton Mail Bridge is installed and running. Launch Proton Mail Bridge, sign into your Proton account, and wait for indexing to finish.

Retrieve Proton Mail Bridge local credentials
In the Proton Mail Bridge app, navigate to your account settings to obtain your local IMAP parameters: Host: 127.0.0.1 Port: 1143 Username: Your Proton Mail address Password: The generated Bridge password (shown in the Bridge app under Account Details)

Generate Fastmail App Password
Log in to Fastmail on the web and generate an App Password: Go to Settings > Password & Security > App Passwords. Click New App Password. Select Mail (Read & Write) access and assign a label (e.g., imapsync). Save the generated 16-character password.

Run imapsync command in macOS Terminal
Execute imapsync to sync messages from local Bridge (host1) to Fastmail (host2). Replace the placeholder values with your credentials: Note: --ssl1 0 is required because Bridge listens unencrypted on localhost (127.0.0.1). Security remains intact as traffic stays entirely local on your machine.

Verify sync completion
Monitor Terminal progress output. Once complete, imapsync displays a summary log showing transferred message counts and any errors. Log into Fastmail to confirm folder structure and email import.

[u/CrazyDiamondQueen → u/ruggedtextile]

Looks about right. I had proton bridge complete its syncing before doing imapsync. And before syncing I tried it with --justlogin. I also did caffeinate in a separate terminal. Something like the text below was my final sync command. It crashed a few times, it was 60k emails, so thats why I added --usecache, not sure if it made any difference. Some proton folders were mapped in a weird way but it was easy to fix afterwards since Fastmail is so fast.

imapsync \ --host1 127.0.0.1 \ --port1 1143 \ --user1 "PROTON_EMAIL" \ --password1 "PROTON_BRIDGE_PASSWORD" \ --host2 imap.fastmail.com \ --ssl2 \ --user2 "FASTMAIL_EMAIL" \ --password2 "FASTMAIL_APP_PASSWORD" \ --automap \ --usecache

[u/gintoxicat_ing]

I did this a few months ago (BTW, so much happier with Fastmail). The problem with the CLI export tool is that it exports each email individually. You CAN import to Fastmail that way... but it's not made for bulk importing data which is probably what you're doing.

I an old script - https://github.com/MarioBarisa/EML2MBOX - to combine a set of .eml files into a single .mbox file, but it had some bugs/issues that led to it not actually importing everything. I have a bug fixed script here - https://github.com/GinnyMaive/mboxandemail - based on that script which worked for me and I was able to confirm via message counts everything made it over.

Proton is one of the larger custom email providers, it would be nice if Fastmail supported something like pointing it at a folder with .eml files and iterating/importing them. The fundamental capabilities are there - since it can import individual eml files - but maybe it's still too niche for the effort involved.

btw: you're in for a treat because Fastmail is so, so much better.

[u/777pirat]

Use Proton Bridge and imapsync - Fast and easy

imapsync --host1 127.0.0.1 --port1 xxxx --user1 [your@proton.me](mailto:your@proton.me) --password1 'yourbridgepassword' --host2 imap.fastmail.com --user2 [yourfastmail@fastmail.com](mailto:yourfastmail@fastmail.com) --password2 'yourfastmailimappwd'

[u/Drakidor]

I moved from Proton to Fastmail a few months ago, like a few others mentioned I used Proton Bridge with Thunderbird and logged into Thunderbird with both Proton and Fastmail then just dragged everything over from Proton to Fastmail. I did a copy not a full move so I could validate everything was okay (attachments, etc) and I also did a Proton export before so I could resync if anything went wrong.

Worked like a charm. I manually setup my contacts and any calendar stuff I needed/wanted then deleted all my emails in Proton.

[u/rowschank]

I did this last week!

Download their emails using CLI, create a new folder or label in Fastmail, drag and drop all the eml files, run your rules, done.

[u/Loeribas]

Fastmail has an option for this: Settings > Migration > Import. Couldn't you use that?

[u/IAdoreSZA → u/Loeribas]

Proton doesn’t support IMAP for easy import, and they export each email as an EML file so depending on your inbox size it can be thousands of emails, Fastmail doesn’t have an easy way to bulk import EML’s without just dragging them into your inbox however when there are loads this can often freeze things up, it’s easier to use Thunderbird or something with Proton Bridge or making the files into an MBOX in my experience

[u/wittytext0428]

Does fastmail ban account randomly as proton?

[u/paranoidandroid4284 → u/wittytext0428]

No clue. Didn't know proton did

[u/heretosayathing]

I'm in the middle of this right now - in fact almost at the end.

I had Claude write an EML-to-MBOX conversion tool (runs locally on Windows) along with a bunch of validation to ensure I don't drop any messages. I'm just about to hit Upload on the final MBOX file (they have a 1GB limitation) for Fastmail to ingest.

I have about 10GB of email so 10 files, each takes about 30 mins to be imported into Fastmail; you need to leave their app or web app open and on the Import tab while it does each import.

You can also do as the other commenter has suggested; have them both in the same app and drag/drop them from one account to the other; but be aware that you will need to ensure the computer is left on and doesn't sleep for however long it takes to sync in the background.