Open Bug 421779 Opened 17 years ago Updated 5 months ago

Support for SMTP BURL extension (RFC 4468)


(MailNews Core :: Networking: SMTP, enhancement)



(Not tracked)


(Reporter:, Unassigned)




(Keywords: perf)

When sending a message, the message is sent to both the SMTP server and the IMAP server for storage in the Sent folder. For large messages or low bandwidths, this may take a long time. For people who pay per megabyte internet traffic, e.g. mobile users, this may expensive as well.

RFC 4468 specifies the BURL extension to SMTP that allows clients to store the message in the IMAP server and then refer to it in the SMTP conversation rather then transferring the whole message over the wire again. Thunderbird should use this extension on SMTP servers that support it.

RFC 4468 is currently a Proposed Standard. It is implemented in Sun Messaging Server 7.0:
Component: General → Networking: SMTP
Product: Thunderbird → Core
QA Contact: general → networking.smtp
Product: Core → MailNews Core
what a concept
Keywords: perf
It seems neither postfix nor exim support this yet. In mean time people usually use gmail style copying in IMAP sent folder after message submitted to SMTP and not copy to IMAP from MUA.
1. bcc self:
   In Account Settings... | tab Copies and Folders
   Disable [ ] Place a copy in ... Folder
   Enable [x] Bcc these email addresses: []
2. Filter:
   In Tools | Message Filters..., create a filter that matches
   From, contains,
   Move message to, Sent

This means you'll still transfer the message twice (once upload with SMTP, once download (instead of upload) with IMAP). However, depending on prefs, the attachment is not downloaded, which is typically the big issue. Also, download is often much faster than upload.
This proposal would:
1. Entirely avoid the duplication
2. Avoid the workaround in last comment,
   2.1. ... which users need to know and set up first
   2.2. The workaround might have other side-effects,
        like triggering on some spam which uses your own address as From
        (hasn't been a problem in practice for me, though, although I use
        this method.)

I would wait for Postfix to implement this first, though.
Dovecot just added support in the core code (for 2.3, due to be released before the end of the year) for BURL/URLAUTH thanks to Stephan Bosch.

It would be awesome if Thunderbird could be one of the first clients that made use of it.

Dovecot 2.3 is out since a while already, so client support could be tested against an actual server. Has any progress happened in Thunderbird to implement this?

Please note, we should not wait for Postfix to implement this.

BURL is an extension to MSA functionality only. It is not applicable to MTA functionality.
Dovecot implements both MDA and MSA.
Dovecot MSA implementation is sufficient for this to work.

The TB Roadmap mentions Better offline and slow network support [TB2021]
This feature request would fit quite well in there.

There probably is an additional advantage with this BURL method: It has happened to me a few times that Thunderbird sends an e-mail over SMTP, and then fails to store it over IMAP (the Yahoo server was probably having trouble at the time). But there may be other failure scenarios, like the laptop running of battery suddenly.

As I result, the message was sent, but I no longer had a copy in the "sent" folder.

With BURL, Thunderbird has to upload the e-mail first, so you probably cannot lose an e-mail after it has been sent.

Some providers, like Yahoo, have changed their behaviour: their SMTP server automatically save a copy of all e-mails sent into your "sent" folder. But that does not seem to be consistent. I could not find proper documentation about it at Yahoo. As a result, most e-mails I sent end up duplicated in the "sent" folder, but not all of them. This kind of mess would probably be history with BURL.

Severity: normal → S3

(In reply to Selek Respa from comment #8)

The TB Roadmap mentions Better offline and slow network support [TB2021]
This feature request would fit quite well in there.

I don't see this on the roadmap anymore, or on the backlog page. Did that goal get dropped? (Interestingly, nothing on the roadmap currently seems to be all that relevant to improving email directly.)

Even on fast networks, this would be a huge boon. A large message with an attachment can take the better part of a minute to send, and then you have to wait for it all over again to do the IMAP APPEND. I think Thunderbird is still in a good position to implement this. Trojita seems to be the only other client (still) I can find that supports this. I will use that in the meantime for testing BURL.

Any such improvement is delayed from earlier estimates. There is no estimate at the present time.

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