Open Bug 1757478 Opened 4 months ago Updated 3 months ago

cannot save large attachments (larger than 21MB)


(MailNews Core :: Networking: IMAP, defect)

Thunderbird 91


(Not tracked)



(Reporter: dxztaurine, Unassigned)



Steps to reproduce:

This issue has been an issue for around a year, I've gotten around to looking into it recently. Outlook (office 365) now is supporting larger files in email protocols, we're seeing 21-30MB files, this is where thunderbird is having issues.

It is very easy to reproduce this, and it works on every OS, your mail server may not support the files that are this big though.

  • email yourself a file that is larger than 21MB, I recommend just .tar ing several files together or something
    (you will get a filelink msg that recommends using that, however the people whom we get the emails from are generally using outlook (office 365) and they do not get this message, obviously, so it is irrelevant here)

  • when you view the email, especially the source, you'll see that it's actually a good email and the base64 encoded file is there, and it works. You can easily copy paste the giant base64 message, save it into a file and run "base64 --decode filename > file.tar" and it'll work, the file works perfectly, this works with any file... thunderbird fails to save it though

  • save the file, it'll save as like 27bytes of data or so, and it won't open, obviously. I've tried every "attachments" addon, it seems they all use whatever thunderbird does internally because they fail as well, I figured at least one would do base64 decode on it's own..

Actual results:

We get a file (anyone on my 17 person team) and can't open it if it's too big

Expected results:

We should be able to save the file since the "view source" has the correct file, but base64 encoded.

I have tested this on:
fairmail (android)
blue mail (android)
outlook (desktop, android, and iOS)
gmail app (android)
all of them work, except thunderbird, with the same emails.

Summary: cannot download large attachments → cannot save large attachments

Is this IMAP?

Summary: cannot save large attachments → cannot save large attachments (larger than 21MB)

Yes it's imap

Sounds familiar.

Component: Untriaged → Networking: IMAP
Product: Thunderbird → MailNews Core

I'll guess that the reporter is not using offline store. If so, setting mail.server.default.mime_parts_on_demand to true may fix it as described here: bug 1673093 comment 13. If that doesn't help, adjustment of the memory cache sizes as described in part 2 may be needed to save big attachments.

See Also: → 1673093

Even though it's already downloaded in the "view source" it can be imap related still? (idk anything at all in how thunderbird operates)

I wrote a program that reads the .eml file and decode the base64 into a file (pretty easy)
I just have the other people at my office right click & save-as the email for now.

Wow thanks, that config setting works great. I'll go add it on some of the co-workers windows machines now.

I can't see how to edit my previous posts to add to them, but I've tested this on the other machines and it works.
I read your other thread too so I set that above back to false and instead just changed the cache because it seems that is less obtrusive since all of our machines have many times more cache than needed... and if the "mime_parts_on_demand" causes any issue with any type of encryption we don't want that.

Also in the other you're talking about how it re-fetches and doesn't re-fetch certain parts etc. I am assuming this is the differences I see in view source or whatever.

What method would you recommend for local storage? Some of the people here like the CEO have 50GB inboxes so we're not syncing to all of the devices. They insist on keeping the inbox to look back years ago if needed.. All I did was double the cache size on everything and it works great.
Would you say I should have in "Synchronization & Storage" -> "disk space" set to "synchronize the most recent 30 days". This would fix the issue as well, from what I understood in your other posts, and solve the issue of not downloading 10+ years of emails.

Thank you for the help & insight.

I can't see how to edit my previous posts ...

There's a little "pencil" icon to the far right of your name so you can edit your post. I do this all the time to correct typos and add more info.

Unless you need to access emails while offline, it's probably better to just keep everything on the server and access it from there. Just my opinion.

But if you want to just store locally the last 30 days that's OK too. Some users are a bit confused by how this works and expect they will only see the emails from the last 30 day. Actually they will all be visible and accessible but only the newer ones (last 30 days) will be stored locally.

Here's a description of how the feature really works: bug 1564421 comment 6.

Probably requires a certain level to edit, mine just has the reply & minimize... I've never made an account here until this thread so

Unless you need to access emails while offline, it's probably better to just keep everything on the server and access it from there. Just my opinion.

Yea, that's how I figured. OK well we just changed the cache on the local office machines (email server is at our office too) & did a "last 5 days" thing+cache on remote computers.

Thanks for all the other reading & threads, I searched google and the bugzilla etc before making this.. obviously didn't search for the right things.

Should I mark this as solved or is it a good reason to update thunderbird's default cache since major players now have bigger email attachment limits or what?

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