SMTP unable to authorize (Stackmail)

I am trialing eM Client on a new Windows 10 laptop and cannot get it to connect to my SMTP server (Stackmail).

When I send mail I get an “incorrect authentication error”. Running diagnose and then fix tells me it has found the server but the password is wrong (it isn’t) and prompts for a new one.

  • IMAP works fine with the same password
  • Windows Mail and Mailbird on the laptop both work fine with the same config
  • Another account in eM Client (VirginMedia) works fine
  • I have tried with Anti-virus (MS Defender) turned off.
  • I have removed and reinstalled eM Client but the problem remains.

I logged a call yesterday with Stackmail but they can find no issues on their end that would cause this. Doing a Google search I see that connecting to SMTP is a common issue with eM Client so I am coming to the conclusion that this is a fault in the product. Windows Mail and Mailbird both worked straight out of the box. Has anyone got any suggestions I haven’t tried? For what it’s worth, I’ve attached a screenshot but note I have tried every combination of settings.

Apart from this issue, this is my favorite of the clients I have tested … but if I can’t SEND email with it I shall have to go with something else.

First and foremost I would suggest you redact the personal info off the screen-shot. Public forum: security.
Also, what eMC licence are you using?

If it’s the Free licence there are restrictions in the use of eMC that may be the problem if you are using Stackmail. See here:

Good point, screenshot redacted.

I am just evaulating clients on a new laptop so at the moment only have the free licence. My hosting company (Lowreg) provides the email service, they happen to use Stackmail at the backend. I’m not clear why that should make a difference to the licence agreement?

I’ve spent another few hours on this and I now understand the problem. The diagnosis logs show that eMC is trying to use CRAM-MD5 to authenticate. From other posts on the forum it seems that nobody has managed to get CRAM-MD5 working from eMC and it can’t be overridden, so it looks like eMC isn’t for me.

I’m really disappointed as this was by far my preferred client.

viernes 18 septiembre 2020 :: 1423hrs (UTC +01:00)

Hi IanW…

These are the settings from Stackmail:

+++++ +++++ +++++ +++++
Account type: IMAP
Incoming mail server:
Outgoing mail server:
Incoming server port (IMAP): 993.
Use the following type of encrypted connection: SSL.
Outgoing server port (SMTP): 587.
Use the following type of encrypted connection: TLS.
+++++ +++++ +++++ +++++

Comparing these with your grapic it appears that you are using
the wrong SMTP Port: you have 465

¡Saludos desde la soleada España!


[email protected]

The Free licence doesn’t allow commercial use of eMC. It requires a Pro licence.

Also, I thought CRAM-MD5 was obsolete.

There are no problems with SMTP and eMC that I’m aware of. It’s certainly the best mail client I’ve tried by a country mile.
Try using port 587 to force SSL/TLS

Thanks for the replies.

Just to reiterate, the screenshot was just an example, in fact it was how the “fix” option left it (“fix” was impressive, by the way, managing to identify the correct servers). I have tried all the ports (25, 465 & 587) and security policy settings, including combinations that shouldn’t work. The diagnostic logs show that the systems are connecting but the authorisation - using CRAM-MD5 - is rejected. I know it’s an obsolete protocol but I have no contol over that and anyway, if it’s in the product it ought to work.

This is the SMTP log using port 587:

16:33:05.634|029|   SMTP C: STARTTLS
SMTP S: 220 TLS go ahead
16:33:05.751|029|   SMTP C: EHLO [n.n.n.n]
SMTP S: Hello [n.n.n.n] [x.x.x.x]
SMTP S: 250-SIZE 52428800
16:33:05.789|029|   SMTP C: AUTH CRAM-MD5
SMTP S: 334 xxxxxxxxxxxxxx
16:33:05.836|029|   SMTP C: xxxxxxxxxxxxx
SMTP S: 535 Incorrect authentication data

I’m not using it commercially. I do have my own domain on a hosting company, which happens to use stackmail, does this constitute commercial use? Even so, I can’t believe the restriction would be implemented by deliberately failing authentication.

I am very impressed with the product (its diagnosis options are unrivalled!). If someone can definitely confirm that this issue goes away with a licence I will happily buy one, but to me this looks like a bug. If you do a forum search on CRAM-MD5 you’ll see there are lots of issues with it.

My flag about the licence was just cautionary. Even if you get the CRAM-MD5 authentication working, experience from past posts here have resulted in Free licences being chopped dead when eMC “powers that be” recognises the potential use as commercial. How it does it I’m not sure, but having your own domain/mail server is probably an indicating factor.

I have no idea why the server has rejected the authentication, so it might be worthwhile trying to contact the Support group for advice here:

Support & bugs - [email protected]

However, because CRAM-MD5 authentication protocol was obsolete over 12 years ago I don’t offer much hope.

That’s the whole point, why is it in the product? I don’t care if they fix it or remove it, either will be fine. My server doesn’t require CRAM-MD5, it is eMC that is choosing to use it (and failing).

I have spent a number of man-hours debugging this product, I would very much like to have bought it but it doesn’t work in my case and there is no value to me in spending any more time on it. It’s a product bug that has existed for at least 10 years and has been reported here a number of times, which reduces my confidence in it somewhat.

Thanks again for your interest.

sábado 19 septiembre 2020 :: 1833hrs (UTC +01:00)

Hi Ian…

How many accounts are you attempting to run with the Free license?
I assume you know there is a limit of TWO.

I also have my own hosted domains and some while back had SMTP
issues, long before I started using EMC with whom I’ve never had
any mail issues.
I overcame the original problem by switching to a 3rd party SMTP
service, also because of ISP connection permissions throughout EMEA.
I have used ‘authSMTP’ for over 15 years, have never had a problem.
I have 116 users on the service throughout my companies.

¡Saludos desde la soleada España!


[email protected]

No that’s incorrect - eMC requests the authentication methods supported by the server and chooses the most secure.

SMTP S: 250-AUTH PLAIN LOGIN CRAM-MD5” - this is SENT from the server.

The server gives eMC a choice of PLAIN or CRAM-MD5 (as above) so eMC has to choose the latter.

It’s almost certainly a problem with the server side processing NOT eMC - but try contacting eMC Support and send them a copy of the log for analysis as suggested.

But, as I advised above. CRAM-MD5 authentication protocol was obsolete over 12 years ago I don’t offer much hope that Support is going to give much attention to this.

If this was a server side issue then why does every other client connect without a problem? I am using Windows 10 Mail, Thunderbird, Mailbird, Android Mail, and Samsung Mail and all are able to send email through this SMTP server. Not to mention my hosting company’s thousands of other customers.

It doesn’t have to choose the latter, it only does so because it thinks it can support it. If it had to, what would be the point of the server sending a list at all?

Many clients allow you to force PLAIN and if eMC had this option I could use it as a workaround, but unfortunately it doesn’t. Note however that I haven’t actually had to do this in any other client, either they use CRAM-MD5 properly or - more likely - they don’t support it and fall back to PLAIN. I don’t know which but it doesn’t matter to me, they work!

The only attention they need give is to take it out, then it will work.

I have sent the log to support. If they can fix this before my 30 day trial expires they will have another customer!

I hope you get your issue resolved. I suspect TB et al work around CRAM-MD5 problems by defaulting to PLAIN or LOGIN, but that opens up all sorts of security exposures.
Anyway, good luck.