On a Yocto-built embedded Linux system, we're trying to send e-mails through 
SMTP with SSL (port 465) or MSA (port 587). We're testing with smtp.gmail.com 
and smtp.zoho.com. We have code that works fine with Windows. But with Mono, 
we're getting System.IO.IOException: The authentication or decryption has 
failed.

We've found on the Mono Security FAQ that we need:

a) to install root certificates using mozroots or similar.
b) to get the intermediate certificates from the SMTPS port 465, using certmgr.

(a) is fine, and we've done that using the Yocto mozroot-certdata package. We 
can confirm that HTTPS works fine after that improvement, using the tlstest 
program.

But (b) is problematic for several reasons:

Firstly, we're puzzled as to why (b) is necessary. It seems that doing HTTPS 
with Mono (e.g. using tlstest program), it doesn't need intermediate 
certificates to be manually loaded--it is able to use the certificates during 
the connection negotiation just fine.

Secondly, on our system we want customers to be able to configure for any SMTP 
server (using a web-browser interface). It's not practical to do step (b) in 
that situation. Certmgr requires interactive operation (typing 'y' to confirm 
individual certificates) which is not a practical interface for end-users. Also 
we've noticed that certmgr shows a warning "WARNING: Certificate signature is 
INVALID" which we think might be incorrect--if so, that makes it impossible to 
verify the validity of the certificates.

Thirdly, step (b) appears to require the use of SMTPS port 465 to get the 
intermediate certificates--we've had no success getting certificates from MSA 
port 587, because the certmgr step also gets System.IO.IOException: The 
authentication or decryption has failed. That means, it is impossible to get 
the intermediate certificates for connecting to an MSA port 587, unless the 
mail server also provides SMTPS port 465 with matching certificates.

So, we're hoping there is some way to improve SMTP with SSL/TLS/MSA etc, so 
that it "just works" without requiring a separate step of acquiring 
intermediate certificates. Is that possible? What is the status of SMTP with 
SSL/TLS in Mono?

-- 
Craig McQueen

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