I’m still having this issue. Will it ever be fixed? 
Having this very issue on 2/6 of my active Gmail accounts. The error started happening after changing the passowrd of the two accounts. It’s fixed by re-linking the accounts to Mailspring through the browser, but then happens again when the PC is restarted.
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Well, although i liked mailspring, this syncing issue drives me crazy. Am gonna forget and move on for now.
And what is worse…it’s there already for quite some time 
Even the previous version had this issue and when the latest version got pushed, the syncing issue was still there???
That part i really don’t get! I would expect if a newer version got pushed that at least that part was solved, but nope.
This issue only seems to happen on my work PC. On my home PC and laptop this doesn’t happen. I’ve tried re-installing but still doesn’t work on my work pc. how is this possible?
Anyone found a solution for this error? how to reach out to Mailspring team? Even for Mailspring Pro… This issue is occuring… Love mailspring this issue is seriously irritating…
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I really like Mailspring but I experienced this problem as well. This unfortunately makes Mailspring unusable for the moment. If anyone is picking this issue up to fix it and needs more information to reproduce, do not hesitate to post here.
Until this is fixed I have to use another mail client.
Do you guys have any solution for this sync error?
I have subscribed to mailspring but i could not find any solution for this error. It is really frustrating. I would really appreciate if you could help on this one? i could not able to reach the support team as well. kindly point me to the right direction if you can…
Please help.
TLDR: If you are a Windows user, try this:
- Go to Credential Manager > Windows Credentials, and remove Mailspring Keys.
- Reconnect your account(s).
I made a custom Mailspring-Sync build to debug token refresh logic, and noticed that the refresh token passed to Mailspring-Sync is not the most recent one. It seems to me that when a user reconnects an account, the credentials are not properly saved into Credential Vault on Windows. On a reboot Mailspring passes an old (and expired) refresh token to Mailspring-Sync, which causes it to fail to refresh the access token.
After I clear the credentials from Credential Vault, the problem seems to be fixed. I have no idea how to reproduce this issue (i.e. why credentials are not updated on reconnect), so I can’t really propose a fix. If someone can let me know under what condition the credential stored in Credential Vault become out of sync, I might be able to take a closer look.
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Thank you. Your solution currently work for me. It solved the Sync problem of Mailspring with my Yahoo Mail and Gmail connection.
The same thing happens to me too.
2 other accounts work OK but this one does not.
17500 [2022-06-18 21:44:34.555] [main] [info] Identity created at 1514455141 - using ID Schema 0
17500 [2022-06-18 21:44:34.556] [main] [info] ------------- Starting Sync (<EMAIL>@gmail.com) ---------------
17500 [2022-06-18 21:44:34.558] [metadata] [info] Metadata delta stream starting...
17500 [2022-06-18 21:44:38.567] [background] [info] Fetching XOAuth2 access token (gmail) for bcfa1827
17500 [2022-06-18 21:44:39.216] [background] [critical]
***
*** Mailspring Sync
*** An exception occurred during program execution:
*** {"debuginfo":"https://www.googleapis.com/oauth2/v4/token RETURNED {\n \"error\": \"invalid_grant\",\n \"error_description\": \"Token has been expired or revoked.\"\n}","key":"Invalid Response Code: 400","retryable":false,"what":"Unknown exception"}
***
Been almost 2 Years - Still frustrated by this sync problem on my mac!
Any suggestions for a closer mail client alternative to mail spring?
The fix is pretty obvious. I am on Fedora 40, and I installed Mailspring (1.13.3) from the application center that uses Flatpak for apps. After every re-login, Mailspring shows a sync error and asks me to re-login to Gmail again.
Why it happens
As it appears, Flatpak creates a temporary filesystem for Mailspring in the sandbox, where the mailbox stores passwords. This temporary filesystem is destroyed after re-login or if you close Mailspring along with all background processes (Ctrl + Q).
How to fix that
Hard way:
If you installed Mailspring from the app center (using Flatpak), you can install an additional package called “Flatseal”, find out where Mailspring stores the keys, and add this path in the “Persistent files” setting in Flatseal.
Easy way:
Remove the Mailspring installation, go to the Mailspring - The best free email app page, click on “Linux (64-bit .deb)” if you are an Ubuntu user, or “Linux (64-bit .rpm)” if you are a Fedora user, then just double-click on the downloaded file and install Mailspring from that file. After that, Mailspring will work correctly, but you will need to do this every time when you want update mailspring to the new version
P.S. Avoid to download snap version, most likely it will have same bug