Thanks for a bug report. It seems to me that the GPG password prompt is cancelled for some reason. It can be that the desktop environment remembers one password prompt cancel and reuses it (Evolution itself does so for its accounts, though the GPG password prompt does not go through this part of the Evolution's code).

Could you run evolution from a terminal like this:
   $ CAMEL_DEBUG=gpg evolution
and then try to send the message with GPG signing enabled and see what was added to the console, if anything, please? The added logging may add some debug output from the GPG call.

I guess the problem is in gpg2 (or gpg) agent settings.

Yeah .., well kind of nice, to hear from you so quickly. That's actually:

> andrew@s55:~$ CAMEL_DEBUG=gpg evolution
> status: [GNUPG:] USERID_HINT 99B6DD316A9364C6 Andreas Glaeser
> <andreas.glaeser@irregulaire.info> status: [GNUPG:] NEED_PASSPHRASE 99B6DD316A9364C6
> 99B6DD316A9364C6 17 0 status: [GNUPG:] ERROR check_hijacking 33554509
> status: [GNUPG:] GOOD_PASSPHRASE
> status: [GNUPG:] BEGIN_SIGNING H8
> status: [GNUPG:] SIG_CREATED D 17 8 00 1432296705
> 7C358ECD7C3C90B570FC02C599B6DD316A9364C6 status: [GNUPG:] USERID_HINT 99B6DD316A9364C6
> Andreas Glaeser <andreas.glaeser@irregulaire.info> status: [GNUPG:] NEED_PASSPHRASE
> 99B6DD316A9364C6 99B6DD316A9364C6 17 0 status: [GNUPG:] ERROR check_hijacking 33554509
> status: [GNUPG:] GOOD_PASSPHRASE
> status: [GNUPG:] BEGIN_SIGNING H8
> status: [GNUPG:] SIG_CREATED D 17 8 00 1432296725
> 7C358ECD7C3C90B570FC02C599B6DD316A9364C6
> 

Evolution also tends to forget mail-account-passwords, although they should be stored in the GNOME-keyring, and entering them once is not sufficient.

I told you, I will use Icedove/Thunderbird, if this Mail-Client doesn't work for me properly.

(In reply to Andreas Glaeser from comment #2)
> [GNUPG:] ERROR check_hijacking 33554509

According to
https://lists.gnupg.org/pipermail/gnupg-commits/2014-April/010458.html
the above error means that gnome-keyring hijacked the gpg-agent to gnupg. It's meant to be a warning only. 

> > status: [GNUPG:] SIG_CREATED D 17 8 00 1432296705

This means that the signing worked properly, thus the message send might be cancelled later. I do not see why, though.

Do you send messages through a SMTP server? If you do, then the next step after the message is being signed is to pass it to the server. Using this debugging option:
   $ CAMEL_DEBUG=smtp evolution
will print debugging from the SMTP transport code.

> Evolution also tends to forget mail-account-passwords, although they should
> be stored in the GNOME-keyring, and entering them once is not sufficient.

Maybe it's one part of the issue with sending, not getting the right password. I cannot tell right now whether it is or it isn't. It just works for me. I sometimes also get some error with passwords, but a restart of all evolution processes (especially of the evolution-source-registry) usually cures the issue, I suspect libsecret not connecting itself to the running gnome-keyring daemon properly or something like that.

> I told you, I will use Icedove/Thunderbird, if this Mail-Client doesn't work > for me properly.

Sure, you always have the freedom to choose the software which works for you. It also makes perfect sense, why would anyone use anything what might not work for him/her properly? I'd appreciate if you would be still willing to investigate what's going wrong on your machine, because, as I said, I do not experience this issue, neither many of other users (otherwise this would be quite hot bug report with many duplicates).

> andrew@s55:~$ CAMEL_DEBUG=smtp evolution
> [SMTP] Connecting to server mail.gmx.net:587 from account 1427119800.16764.10@s5
> [SMTP] received: 220 gmx.com (mrgmx101) Nemesis ESMTP Service ready
> [SMTP] sending: EHLO s55.lokal
> [SMTP] received: 250-gmx.com Hello s55.lokal [95.91.214.189]
> [SMTP] received: 250-SIZE 69920427
> [SMTP] received: 250-AUTH LOGIN PLAIN
> [SMTP] received: 250 STARTTLS
> [SMTP] sending: STARTTLS
> [SMTP] received: 220 OK
> [SMTP] sending: EHLO s55.lokal
> [SMTP] received: 250-gmx.com Hello s55.lokal [95.91.214.189]
> [SMTP] received: 250-SIZE 69920427
> [SMTP] received: 250 AUTH LOGIN PLAIN
> [SMTP] sending: AUTH LOGIN
> [SMTP] received: 334 VXNlcm5hbWU6
> [SMTP] sending: YWdsYWVzZXIxQGdteC5uZXQ=
> [SMTP] received: 334 UGFzc3dvcmQ6
> [SMTP] sending: PXF1b3JOd29yTi0uNw==
> [SMTP] received: 235 Authentication succeeded
> [SMTP] Sending with server mail.gmx.net:587 from account 1427119800.16764.10@s5
> [SMTP] sending: MAIL FROM:<andreas.glaeser@irregulaire.info>
> [SMTP] received: 550-Requested action not taken: mailbox unavailable
> [SMTP] received: 550 Sender address is not allowed.
> [SMTP] sending: QUIT
> [SMTP] received: 221 gmx.com Service closing transmission channel
> 
> (evolution:10887): GLib-GIO-CRITICAL **: g_network_address_set_addresses: assertion 'addresses != NULL && addr->priv->sockaddrs == NULL' failed
> [SMTP] Connecting to server server12.server-core.de:25 from account 1427798982.5962.10@s5
> [SMTP] received: 220 server12.server-core.de ESMTP Postfix
> [SMTP] sending: EHLO s55.lokal
> [SMTP] received: 250-server12.server-core.de
> [SMTP] received: 250-PIPELINING
> [SMTP] received: 250-SIZE 26214400
> [SMTP] received: 250-ETRN
> [SMTP] received: 250-STARTTLS
> [SMTP] received: 250-AUTH PLAIN LOGIN CRAM-MD5
> [SMTP] received: 250-AUTH=PLAIN LOGIN CRAM-MD5
> [SMTP] received: 250-ENHANCEDSTATUSCODES
> [SMTP] received: 250 8BITMIME
> [SMTP] sending: STARTTLS
> [SMTP] received: 220 2.0.0 Ready to start TLS
> [SMTP] sending: EHLO s55.lokal
> [SMTP] received: 250-server12.server-core.de
> [SMTP] received: 250-PIPELINING
> [SMTP] received: 250-SIZE 26214400
> [SMTP] received: 250-ETRN
> [SMTP] received: 250-AUTH PLAIN LOGIN CRAM-MD5
> [SMTP] received: 250-AUTH=PLAIN LOGIN CRAM-MD5
> [SMTP] received: 250-ENHANCEDSTATUSCODES
> [SMTP] received: 250 8BITMIME
> [SMTP] sending: AUTH LOGIN
> [SMTP] received: 334 VXNlcm5hbWU6
> [SMTP] sending: YW5kcmVhcy5nbGFlc2VyQGlycmVndWxhaXJlLmluZm8=
> [SMTP] received: 334 UGFzc3dvcmQ6
> [SMTP] sending: YmFuR3dvbkc/PQ==
> [SMTP] received: 235 2.7.0 Authentication successful
> [SMTP] Sending with server server12.server-core.de:25 from account 1427798982.5962.10@s5
> [SMTP] sending: MAIL FROM:<andreas.glaeser@irregulaire.info>
> [SMTP] received: 250 2.1.0 Ok
> [SMTP] sending: RCPT TO:<aglaeser1@gmx.net>
> [SMTP] received: 250 2.1.5 Ok
> [SMTP] sending: DATA
> [SMTP] received: 354 End data with <CR><LF>.<CR><LF>
> [SMTP] sending: \r\n.\r\n
> [SMTP] received: 250 2.0.0 Ok: queued as 8375212404B8
> [SMTP] sending: QUIT
> [SMTP] received: 221 2.0.0 Bye

Hope this helps.

Thanks for the update, just do not copy passwords in the public; you can, in certain cases, expose them in the wild.

(In reply to Andreas Glaeser from comment #4)
> > [SMTP] Sending with server mail.gmx.net:587 from account 1427119800.16764.10@s5
> > [SMTP] sending: MAIL FROM:<andreas.glaeser@irregulaire.info>
> > [SMTP] received: 550-Requested action not taken: mailbox unavailable
> > [SMTP] received: 550 Sender address is not allowed.
> > [SMTP] sending: QUIT
> > [SMTP] received: 221 gmx.com Service closing transmission channel

The above shows that the server rejected the send. It wasn't the evolution. Then I suppose you retried:

> > [SMTP] sending: MAIL FROM:<andreas.glaeser@irregulaire.info>
> > [SMTP] received: 250 2.1.0 Ok

and it succeeded and the message was properly sent.

I do not know why the server rejected the initial MAIL FROM, they both look identical to me, thus it would be good to ask the mail server support or administrators to investigate why they say so.

I think some servers can have a policy to not allow multiple connections at once, like when you connect using a Web interface, then the sending (SMTP) can be disabled. I do not know whether this is the case here too.

In any case, the log shows that there cannot done anything on the evolution side, at least the captured communication doesn't show anything obviously wrong, epsecially when the authentication succeeded in both cases.

The first part of the debug-output, before the blank line actually appeared directly upon entering the camel-debug-command, there was nothing done from the user-side yet.

The second part shows enabling the server-core-account and trying to send the test-mail to the gmx-account.
You are right, the test-message was actually really sent, but the window, it was written in, stayed open, with the error-message, I told you initially.
Some people outlined to me already, they received messages for four times, because I retried sending them several times and they seemed not to be sent.
Are you getting the idea, why I don't want to go on using Evolution??

(In reply to Andreas Glaeser from comment #6)
> The first part of the debug-output, before the blank line actually appeared
> directly upon entering the camel-debug-command, there was nothing done from
> the user-side yet.

It can be that a message in On This Computer/Outbox was send (tried to be sent). I do not see any other reason why the SMTP server would be contacted right after start.

> The second part shows enabling the server-core-account and trying to send
> the test-mail to the gmx-account.
> You are right, the test-message was actually really sent, but the window, it
> was written in, stayed open, with the error-message, I told you initially.

Right, with the "Sending message (cancelled)".

> Are you getting the idea, why I don't want to go on using Evolution??

Right, though what you see is not a normal behaviour.

Once the message was sent, it is saved into the Sent folder. Could you verify what Sent folder you've setup in the account properties, in the Default tab? What if you change it to something else? I think the window can cheat in certain cases, thus the best to pick some random folder and then back to the correct Sent folder, just to make sure that the value of the Sent folder had been changed and will be saved. The default Sent folder is On This Computer/Sent. The other account might have setup a different Sent folder, I believe.

> --- Comment #7 from Milan Crha <mcrha@redhat.com> ---
> (In reply to Andreas Glaeser from comment #6)
> > The first part of the debug-output, before the blank line actually appeared
> > directly upon entering the camel-debug-command, there was nothing done from
> > the user-side yet.  
> 
> It can be that a message in On This Computer/Outbox was send (tried to be
> sent). I do not see any other reason why the SMTP server would be contacted
> right after start.
> 
> > The second part shows enabling the server-core-account and trying to send
> > the test-mail to the gmx-account.
> > You are right, the test-message was actually really sent, but the window, it
> > was written in, stayed open, with the error-message, I told you initially.  
> 
> Right, with the "Sending message (cancelled)".
> 
> > Are you getting the idea, why I don't want to go on using Evolution??  
> 
> Right, though what you see is not a normal behaviour.
> 
> Once the message was sent, it is saved into the Sent folder. Could you verify
> what Sent folder you've setup in the account properties, in the Default tab?
> What if you change it to something else? I think the window can cheat in
> certain cases, thus the best to pick some random folder and then back to the
> correct Sent folder, just to make sure that the value of the Sent folder had
> been changed and will be saved. The default Sent folder is On This
> Computer/Sent. The other account might have setup a different Sent folder, I
> believe.

I had set up the Sent-folder on the server@irregulaire.info, upon changing the Sent-folder location to the local folder, sending of my test-message worked, when reverting the setting to the remote folder, I see the same problem again.

Does this mean, it is actually a problem with the mail-server, so should I actually contact the server-support ??

Is the account configured as an IMAP account? We can debug it to know better, just set the folder back to the .info account, then run evolution from a console as this:
   $ CAMEL_DEBUG=imapx:io evolution &>log.txt
ideally with all other IMAP accounts disabled, thus the log will not contain unnecessary information.

Once the initial update finishes compose the email, send it for example to yourself, and watch the log what will be added. There is no need to see the above output, the only interesting is that after the message was sent. maybe to better identify the place you can turn on both IMAP and SMTP debuggins:
   $ CAMEL_DEBUG=imapx:io,smtp evolution &>log.txt
then seearch the log for the [SMTP] marker and a similar output as in comment #4.

Created attachment 304255 [details]
gzipped out put from $ CAMEL_DEBUG=imapx:io evolution &>debug-log-2.txt

Debug-output added as attachment, I am bad at seeing what's really relevant there, sorry. [debug-log-2.txt.gz]

Thanks for the update. Even I do not see an APPEND command being invoked, the log shows that there are some issues caused by the IMAPx provider:
> BAD Error in IMAP command SELECT: Invalid QRESYNC known-uids
It's shown there multiple times. I suppose if you disable the Quick Resync in the account Properties then you'll be able to store the sent messages on the server for that account too. I suggest to restart the Evolution after such change, just to make sure the new settings are in the effect.

If it'll work, then the reason is bug #719328.

Yes right, it's the quick-resync option, but this is misleading, because it is actually a mail-receiving option in the account settings.
It means this is a minor issue only, also for Debian.