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Forum Discussion

huzer1's avatar
huzer1
Icon for Nimbostratus rankNimbostratus
Jan 13, 2022

SMTP Proxy to Office 365

I'm trying to setup a proxy for SMTP going to smtp.office365.com. I've searched for SMTP documentation, the only one I've come across is quite dated with a version cap of 13.0. But using this as a re...
Niels_van_Sluis's avatar
Niels_van_Sluis
Icon for MVP rankMVP
Jan 14, 2022

Just did a test myself, and it seems to work without a client SSL profile and without the default SMTP profile.

ltm virtual vs_smtp.office365.com {
    creation-time 2022-01-14:14:51:58
    destination 192.168.178.200:smtp
    ip-protocol tcp
    last-modified-time 2022-01-14:14:58:00
    mask 255.255.255.255
    pool pool_smtp.office365.com
    profiles {
        f5-tcp-progressive { }
    }
    serverssl-use-sni disabled
    source 0.0.0.0/0
    source-address-translation {
        type automap
    }
    translate-address enabled
    translate-port enabled
    vlans {
        VM_Network
    }
    vlans-enabled
    vs-index 12
}

And here the output of a basic test:

$ telnet 192.168.178.200 25
Trying 192.168.178.200...
Connected to 192.168.178.200.
Escape character is '^]'.
220 AM4PR0501CA0048.outlook.office365.com Microsoft ESMTP MAIL Service ready at Fri, 14 Jan 2022 13:58:47 +0000
ehlo van-sluis.nl
250-AM4PR0501CA0048.outlook.office365.com Hello [82.174.94.206]
250-SIZE 157286400
250-PIPELINING
250-DSN
250-ENHANCEDSTATUSCODES
250-STARTTLS
250-8BITMIME
250-BINARYMIME
250-CHUNKING
250 SMTPUTF8
quit
221 2.0.0 Service closing transmission channel
Connection closed by foreign host.
$

It seems smtp.office365.com requires STARTTLS, see: https://support.microsoft.com/en-us/office/pop-imap-and-smtp-settings-8361e398-8af4-4e97-b147-6c6c4ac95353. The email client should take care of this itself.