Technical Tip: Configure Microsoft Office 365 SMTP as Mail server in FortiAuthenticator

Make sure to enable Authenticated SMTP. You can find this setting at Org settings > Modern authentication.

Source: https://community.fortinet.com/t5/FortiAuthenticator/Technical-Tip-Configure-Microsoft-Office-365-SMTP-as-Mail-server/ta-p/214959

This article describes how to configure Microsoft Office 365 as a mail server in FortiAuthenticator.

To allow 2FA authentication, configure mail server settings in FortiAuthenticator.
In order to use Microsoft Office 365 mail server, there are some extra steps that need to be configured to allow email from FortiAuthenticator.

FortiAuthenticator is not pre-loaded with Microsoft and other service providers’ certificates, therefore the first step is to add Certificate Chain in FortiAuthenticator as a trusted CAs manually.

Follow the steps mentioned below to download and import the certificate in FortiAuthenticator before starting to configure email settings.

To get the certificate of Microsoft Office 365.

1) Download and install OpenSSL on any Windows machine.

2) Navigate to the OpenSSL directory and execute this command.

In this example, OpenSSL is installed in C:\.

– Ensure that the right directory is used to execute this command.

3) C:\OpenSSL-Win32\bin> openssl.exe s_client -connect smtp.office365.com:587 -starttls smtp
CONNECTED(0000018C)
depth=1 C = US, O = DigiCert Inc, CN = DigiCert Cloud Services CA-1
verify error:num=20:unable to get local issuer certificate
—
Certificate chain
0 s:/C=US/ST=Washington/L=Redmond/O=Microsoft Corporation/CN=outlook.com
i:/C=US/O=DigiCert Inc/CN=DigiCert Cloud Services CA-1
1 s:/C=US/O=DigiCert Inc/CN=DigiCert Cloud Services CA-1
i:/C=US/O=DigiCert Inc/OU=www.digicert.com/CN=DigiCert Global Root CA
—
Server certificate
—–BEGIN CERTIFICATE—–
MIIIpDCCB4ygAwIBAgIQCKADw/Or6WqnCIVhHvaGQjANBgkqhkiG9w0BAQsFADBL
MQswCQYDVQQGEwJVUzEVMBMGA1UEChMMRGlnaUNlcnQgSW5jMSUwIwYDVQQDExxE
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HqZj57jM5ME=
—–END CERTIFICATE—–
subject=/C=US/ST=Washington/L=Redmond/O=Microsoft Corporation/CN=outlook.com
issuer=/C=US/O=DigiCert Inc/CN=DigiCert Cloud Services CA-1
—
No client certificate CA names sent
Client Certificate Types: RSA sign, DSA sign, ECDSA sign
Requested Signature Algorithms: 0x04+0x08:0x05+0x08:0x06+0x08:RSA+SHA256:RSA+SHA384:RSA+SHA1:ECDSA+SHA256:ECDSA+SHA384:

ECDSA+SHA1:DSA+SHA1:RSA+SHA512:ECDSA+SHA512
Shared Requested Signature Algorithms: RSA+SHA256:RSA+SHA384:RSA+SHA1:ECDSA+SHA256:ECDSA+SHA384:ECDSA+SHA1:DSA+SHA1:RSA+SHA512:

ECDSA+SHA512
Peer signing digest: SHA256
Server Temp Key: ECDH, P-384, 384 bits
—
SSL handshake has read 4379 bytes and written 379 bytes
Verification error: unable to get local issuer certificate
—
New, TLSv1.2, Cipher is ECDHE-RSA-AES256-GCM-SHA384
Server public key is 2048 bit
Secure Renegotiation IS supported
Compression: NONE
Expansion: NONE
No ALPN negotiated
SSL-Session:
Protocol : TLSv1.2
Cipher : ECDHE-RSA-AES256-GCM-SHA384
Session-ID: 7C0000005C44F21989E7A7385F296969267B7E51E2AF383CBF7AF8FCB88E3BD9
Session-ID-ctx:
Master-Key: F64BF52AA75F4CD9E331D6F84E4AB38A0218D628D677442707877B90D1EDFB495C2726B

B284FDBF20DD58CEB7D7EAAE9
PSK identity: None
PSK identity hint: None
SRP username: None
Start Time: 1655461985
Timeout : 7200 (sec)
Verify return code: 20 (unable to get local issuer certificate)
Extended master secret: yes
—
250 SMTPUTF8
451 4.7.0 Timeout waiting for client input [AS9PR06CA0739.eurprd06.prod.outlook.com]
read:errno=0

4) Copy and Paste from ‘—–BEGIN CERTIFICATE—–’ to ‘—–END CERTIFICATE—–’ including ‘—‘ signs to notepad and save the file as .CER extension.

5) Open the Certificate file, which is just created in the above step and select the ‘Certification Path’.

Export Intermediate Certificate.

6) Now from here select the Intermediate certificate, in this case, ‘DigiCert Cloud Services CA-1’. Export the certificate and save it.

Select Browse and save this Certificate file.

Select Finish to complete the Export Wizard and then select OK to complete.

Export Root Certificate.

7) Now from here select the Root Certificate, in this case, ‘DigiCert Cloud Services CA-1’. Export the certificate and save it.

Select Browse and save this Root Certificate file.

8 ) Import these Root and Intermediate Certificates to Trusted CAs in FortiAuthenticator.

Logon to FortiAuthenticator and navigate to Certificate Management -> Certificate Authorities ->Trusted CAs -> Select Import to add both Root and Intermediate CAs and select OK.