Issue configuring Proton SMTP in Emby

[Lun 4]

Hi everyone

Since Proton decided to start offering an SMTP service (for some subscriptions), I thought I would try it out to move away from my current Proton Bridge setup. I followed the instructions (https://proton.me/support/smtp-submission) and changed my current settings to the new data but I'm getting the following error:

"Mailbox name not allowed. The server response was: 5.7.1 : Sender address rejected: not logged in"

As anyone faced this issue before? Where in Emby can I see further details on what is exactly failing or how is Emby trying to initiate the connection?

Emby version: 4.9.1.80

 

Thank you in advance.

[pwhodges 2012]

Emby will not give you more information, as that message is from the Proton mail server and Emby has just passed it on.  I guess you need to double-check the SMTP settings in Emby against the Proton instructions, with particular reference to the login.

Paul

[Lun 4]

Thanks for the quick reply.

I did doublecheck and it is all according to their instructions. Unfortunately, there is no mention of this specific error in their documentation as well.

I've already reached out to their support and I'll see what I get back and update this thread (might be useful for other people).

[Kyrunner 86]

2 hours ago, Lun said:

Thanks for the quick reply.

I did doublecheck and it is all according to their instructions. Unfortunately, there is no mention of this specific error in their documentation as well.

I've already reached out to their support and I'll see what I get back and update this thread (might be useful for other people).

I tried to set this up also with the same setup using the plugin proton doesn’t work with the plugin. I created a python script with an api to emby and works great. 

I have a cron  job that runs every morning with new media added and it uses proton smtp to send emails to the users in my script.Here  is an example email.  I even say if it’s is a physical or strm release with a link to IMDb.

Emby Daily Report - New Media Added

Report for the last 24 hours • Generated on 2025-10-29 05:00:01

Movies (5 new)

123 (1999) Physical 

Type: Movie • 6.9 • Drama

Once called  for his efforts to rescue lives, of those he failed to save around every turn. He has tried everything he can to get fired, calling in sick, delaying taking calls where he might have to face one more victim he couldn't help, yet cannot quit the...

 

123 (2024) STRM

Type: Movie • 8.4 • Science Fiction, Adventure

Follow the mythic journey of as he unites with  while on a path of revenge against the conspirators who destroyed his family. Facing a choice between the love of his life and the fate of the known universe,  endeavors to prevent a 

 

 

 

 

 

Edited October 29, 2025 by Kyrunner

[Luke 42077]

The "Sender address rejected: not logged in" error means your email client or application is trying to send an email from an address that is not authenticated with the mail server. To fix this, you need to enable SMTP authentication in your email program's settings and ensure your login credentials (username and password) are correct. 

[Kyrunner 86]

36 minutes ago, Luke said:

The "Sender address rejected: not logged in" error means your email client or application is trying to send an email from an address that is not authenticated with the mail server. To fix this, you need to enable SMTP authentication in your email program's settings and ensure your login credentials (username and password) are correct. 

@LukeAuthentication is performed by the token from Proton when the SMTP relay is created. That's the only authentication is when the token is created, so for username and password, the password would be the token. The SMTP username is the email it's coming from. I believe the issue is with the port Proton uses, secure port 587 and smarttls. 

How to set up SMTP to use business applications or devices with Proton Mail | Proton

 

[Painkiller88 248]

9 minutes ago, Kyrunner said:

@LukeAuthentication is performed by the token from Proton when the SMTP relay is created. That's the only authentication is when the token is created, so for username and password, the password would be the token. The SMTP username is the email it's coming from. I believe the issue is with the port Proton uses, secure port 587 and smarttls. 

How to set up SMTP to use business applications or devices with Proton Mail | Proton

 

As i see you wrote that you made your own script, coding seems not a problem to you, have you tried to make a simple sendmail or other command to send a mail via comandline?

just to see if this works or if there is a problem in general and maybe you are using wrong infos/settings

[Lun 4]

As @Kyrunnermentioned, the configuration on the proton side is fairly limited and I know that the address exists and is capable of sending emails because right now it is working using the proton bridge. (I configured Emby to use the bridge instead of the online smtp server).

The script approach is quite interesting but it goes on the low priority to-do list for now 

[Lun 4]

So, Proton got back to me with the following:

This error means your third-party system skipped the AUTH PLAIN/AUTH LOGIN and Credentials (username and password) steps.
This usually happens when the third-party system does not support AUTH PLAIN/AUTH LOGIN or has a system bug.
You can provide the following information to the developers of the third-party system and ask them to investigate further.

 --- Technical Details --- 

Your system skipped the AUTH PLAIN/ AUTH LOGIN and Credentials commands and directly jumped to the MAIL FROM command.
Therefore, Proton's SMTP Submission server told you, "You have not logged in to the sender account."
You can (1) check if your mail system supports AUTH PLAIN/ AUTH LOGIN and (2) check the Classes and Functions related to AUTH PLAIN/ AUTH LOGIN and the Credentials. Find out why your system skipped these two steps.
A normal SMTP Submission (client to server) process should look like this:

    EHLO mail.*****.com AUTH PLAIN (or AUTH LOGIN)    <----  Your system skipped this step Credentials   <----  And this step MAIL FROM: <***> RCPT TO: <***> ... .. .

 --- End of the Details --- 

Please feel free to let us know if you and the third-party developers require further clarification. Thank you.

@LukeIs this something that could be changed?

Thanks!

[Luke 42077]

Did you configure your smtp credentials?

[Kyrunner 86]

Just now, Luke said:

Did you configure your smtp credentials?

@LukeProton is free maybe it might be easier to spin up a free account and test. The SMTP credentials are the Token that’s created and the email address 

[Lun 4]

@LukeYes, I did. Exactly as documented by Proton and Emby doesn't allow anything else to be configured.

@KyrunnerIt is free but if I'm not mistaken SMTP token usage is not available to the free tier.

[Luke 42077]

Maybe you need to set a different smtp port?

[Lun 4]

What would you suggest?

I tried with 25, 587 and even the legacy 465 (which times out, as it should).

 

These are the instructions from Proton:

 

Am I missing any steps here?

[Q-Droid 989]

Which email address are you using in the "SMTP username" field? It should be the Proton email account for which you generated the token.

You could try entering the same email address in the "email from" field if you haven't already.

 

 

Edited October 31, 2025 by Q-Droid

[Q-Droid 989]

3 hours ago, Lun said:

@LukeYes, I did. Exactly as documented by Proton and Emby doesn't allow anything else to be configured.

@KyrunnerIt is free but if I'm not mistaken SMTP token usage is not available to the free tier.

What OS are you running?

 

[Lun 4]

@Q-DroidIt is the same on both fields and it is the same that Proton provides. When you are creating the token it allows you to select one of your configured domains and it also has a drop down for the specific email account that would be authorize to use and send the emails. (which is the same I'm filling out in Emby).

This instance of Emby is running on a Windows Server.

[Q-Droid 989]

Any specific reason you want to move away from the Proton Mail Bridge? A server wide mail relay seems more convenient than using individual app configs.

 

[Luke 42077]

It also could be this:

Quote

If the EnableSsl property is set to true, and the SMTP mail server does not advertise STARTTLS in the response to the EHLO command, then a call to the Send or SendAsync methods will throw an SmtpException.

 

[Lun 4]

@Q-DroidI would still have it a single config, because the user that would receive it, would distribute it accordingly. I would be removing the need for the Proton Bridge and and email client in the background.

@LukeThank you for the information. I have sent it to Proton to see if this is something that can be configured/changed.

[Luke 42077]

7 hours ago, Lun said:

 

@LukeThank you for the information. I have sent it to Proton to see if this is something that can be configured/changed.

Please let us know what they say. Thanks.

[Lun 4]

@Luke This was Proton's reply:

Please note that the SMTP server (Proton in this case) only responds to commands and never initiates them. So, if STARTTLS is not being used even though Proton supports it, that would mean Emby is not sending the STARTTLS command after the EHLO handshake.
 
The sequence goes roughly like this:

1.  Emby connects to the SMTP server (e.g., on port 587).
2.  Emby sends an EHLO command to identify itself.
3.  The SMTP server replies with a list of supported features, including STARTTLS.
4.  If `EnableSsl = true` is configured, Emby should then send the STARTTLS command to upgrade the connection to a secure, encrypted channel before sending any credentials or message data.

 
Why do I receive the error?
Emby is skipping the STARTTLS command even though the server advertises it.
 
Solutions:

1.  Try using SSL with port 465 to connect without requiring STARTTLS.
2.  Contact Emby support to confirm that their system explicitly sends the STARTTLS command after the EHLO response when `EnableSsl = true` is enabled, for example:
    
        SmtpClient client = new SmtpClient("mail.example.com", 587);client.EnableSsl = true; // Will issue STARTTLS after EHLO if the server supports it

As mentioned before, I did try it on port 465 without success. 

Edited November 5, 2025 by Lun

[Luke 42077]

If there’s an issue then it’s in the dotnet SmtpClient as we’re just configuring it with the values you entered and then telling it to send mail.

[Lun 4]

Then I believe there is nothing else we can do from the Emby side.

I'll keep following it up with Proton to see if there is something that can be done from their side, but I'm not expecting much.

 

Thanks for all the replies!