Problem Email Server

Hi all

I have Synology NAS send me notification email on my mail server running on Nethserver, some NAS of my customer especially with DSM version 6.x or above i have no problem, with version 5.x when i configure notifications email i receive this error:
if i check on server side in the mail log i see this:

It seems a problem with the negotiation of protocol

Did you asked to Synology to support TLS version 1.2 for 5.x DSM?

I think synology not implement tls on DMS 5.x only for me:)
is there a workaround?
I try to use port 25 without secure connection but i receive now this error:

But the authentication is enable as you can see here:

Does the NAS have a public/static ip address?
For non-TLS connection, port is 587
but the TLS policy
might “pretend” a STARTTLS connection.
However… some exceptions can be written into relay section of the emailserver (configuration → details).

Hi Pike

So it’s not possibile to use smtp without secure conneciont using port 25?

On the documentation there’s already the answer.
IMVHO, since 10 years at least, 25 port is not a good option from client to server.

I now using port 25 is not secure option but for this email notification from the nas is only for backup result or state of the RAID so it’s ok using port 25.
Anyway if i use port 587 or 25 i don’t receive the error on client side but on mail server i see this LOG:

If i try without checking secure connection:

I receive this error:


If you want to use Port 25 with authentification, it can be set in Email → Relay:

This uses TLS (Not SSL), so be sure to set your TLS Settings as needed.

A Synology should be able to use this…
I have it working, but the Synology is at a site without NethServer, and accesses my NethServer (In the Cloud) to send status / warning mails…

My 2 cents

The synology you use, @Andy_Wismer which version of DSM use?


Hi Michael

It’s now DS 7.11, but was already working with DSM 6.x (latest)…
Version 5.x will likely have issues…

It used to be a DS918+, but now it’s a DS1518+ model.
(The client needed more disk-space…)

The older model is now at home, taking backups from the office (A doctors practice…).

My 2 cents

Which means you have no case working with DSM 5.x, like @Denis_Pollini have.

I eliminated 10 years old devices at the end of 2020, there were still two clients using very old NAS, as “second” Backup, or Backup of the primary NAS… (DS110…)

DSM 5.x is only used on 10y old NAS, as newer Synos can get 6.x or even 7.x without issues.

The old NAS also caused issues with Win10/Win11.

Let me guess: SMBv2 not implemented?


No options for that, you’re right…



With DSM 5.x is possible to enable smb 3.x as you can see, but i need to fix the email problem…

1 Like

i check this option:

But on Mail Server log i see the same error:

If i put the public ip of the client:

And on the nas this configuration it works!!!


It MAY be possible even with that old box to send mails…

The trick is not to think of that NAS as a client (Like a PC) sending mails, but as another SMTP mail server…

Since the NAS has only to send mail to one address (That in turn can forward mails to other mail…), it will work without authentification…
After all, the whole world ( can send mail to your server - without authentification.

Nethserver will handle mails to it’s domain without authentification!

Test it!

My 2 cents

Hi Andy

I don’t understand so i need to install smtp server on NAS?

No, you have already done it right.

Not using authentification on your Nethserver, for Port 25…
And no TLS / SSL from your NAS…

My 2 cents

Ok thanks you :wink: