ptt is a suit of tools to deploy a full SMTP service. The current available design is:

                                         [ Primary DNS server ]
					           |
                                                   |
 *:465 [ Submission server ] -- TLS --> *:25 [ DKIM signer ] -.
                |                                             |
                ----------------------- [ SMTP relay ] *:25 <-'
       [ Git Database ]                    |  |
			 [ DNS Resolver ] -'  `-> *:25 [ Internet ]

3 unikernels (with [MirageOS][mirage]) exist:

• a submission server (LIPAP) which must be synchronized with a database (such as [irmin][irmin] x [git][ocaml-git]) to authentify users
• a DKIM signer (NEC) which requires a private RSA key and update the primary DNS server of the domain-name with the public RSA key. It signs incoming emails and pass them then to the SMTP relay
• the SMTP relay (MTI-GF) which will resolves recipients via a specific DNS resolver and send incoming emails to destinations.

Even if we use the *:25 to communicate between each unikernels, all of them start a TLS session. Only yhe SMTP relay requires a DNS resolution process and the DKIM private key is never shared to anyone - only the public key is sended to the primary DNS server to let recipients to verify outcoming emails.

This is the usual design of an SMTP service to be able to send an email. The reception of an email does not exists - and it's not the purpose of ptt which does not (yet) implement IMAP.

ptt provides these unikernels and they can be deployed as a simple MirageOS:

• as a simple executable (see mirage configure -t unix)
• as a full operating system

Currently, ptt is used as a full operating system with the hvt target. We deploy these unikernels via KVM & Solo5. DNS resolver and primary DNS server are unikernels too (see [robur.io][roburio] -- but, as far as we can say, this SMTP stack is usable with a simple DNS server (as far as it implements nsupdate).

ptt is not yet stable or reliable but we currently try to deploy/use it and improve it. Don't use it!

ptt has received funding from the Next Generation Internet Initiative (NGI) within the framework of the DAPSI Project.