Sending mail via mailbox.org on mobile connection fails with 501 SMTP error

[ghost]

I have a mail account at mailbox.org. When I am using BlitzMail on my mobile connection (as opposed to my home wlan), I always get the following error message:

Der Server antwortete mit folgendem Fehlder: Bitte überprüfen Sie die SMTP-Einstellungen. 501 Syntax: HELO hostname

Sending mail via k-9 works with the same account on any connection.

This is on version 0.6

[grote]

Is it possible that this is a duplicate of issue #21?

[ghost]

I don't believe so. In my case, the error message is really consistent, retrying does not make any difference. It's also a different message.

I've written now to the mailbox.org support, asking them to contribute any information they could have about the issue.

[grote]

That would be nice. When they have the exact time of your connection attempt, they should be able to get more information about why the message was rejected from their web server logs.

[ghost]

I did recently have problems with another provider and HELO, seems more servers are now checking that HELO is something what they consider "meaningful". Since mobile networks mostly have transparent proxies and NAT this is quite easy to get wrong:(

[grote]

This is also related to #25. Maybe somebody wants to figure out a way for how to get the proper hostname to use in the HELO message?

[duckdalbe]

I have the same problem with my own mail-server. Debugging via the MTA showed me that BlitzMail apparently sends only EHLO without any argument. That finding contradicts #25.

Does BlitzMail actually send EHLO without argument? Or might this be due to network operators filtering headers? It happends also when I tell BlitzMail to use TLS and authentication credentials, though.

Update: this happens also through Wifi-connections, so the network operators probably are not to blame.

Debugged using BlitzMail version 0.6 from f-droid.

[grote]

Does BlitzMail actually send EHLO without argument?

BlitzMail uses libraries to do the sending. I am not sure what it actually sends. I'd be happy for anyone to debug this further.

[ghost]

The library should do the right thing by default and send the localhostname. It does so only erratically (at least in my case). Since DNS is asyncronous this looks like a timing issue.

It works almost always when I invoke apps/BlitzMail send queued. It wokrs almost never when passed through an intent. What is the relevant difference here?

Unrelated but interesting anyway: https://www.javacodegeeks.com/2014/06/javamail-can-be-evil-and-force-you-to-restart-your-app-server.html