ToxMail Experiment Cont'd

I started the other day experimenting with Tox to build a secure e-mailing system. You can read my last post here.

To summarize what Toxmail does:

  • connects to the Tox network
  • runs a local SMTP and a local POP3 servers
  • converts any e-mail sent to the local SMTP into a Tox message

The prototype is looking pretty good now with a web dashboard that lists all your contacts, uses DNS lookups to find users Tox Ids, and has a experimental relay feature I am making progress on.


DNS Lookups

As described here, Tox proposes a protocol where you can query a DNS server to find out the Tox ID of a user as long they have registered themselves to that server.

There are two Tox DNS servers I know about: and

If you register a nickname on one of those servers, they will add a TXT record in their DNS database. For example, I have registered tarek at and people can get my Tox Id querying this DNS:

$ nslookup -q=txt

Non-authoritative answer: text = "v=tox1\;id=545325E0B0B85B29C26BF0B6448CE12DFE0CD8D432D48D20362878C63BA4A734018C37107090\;sign=u+u+sQ516e9VKJRMiubQiRrWiVN0Nt98dSbUtsHBEwYiaQHk2T8zAq4hGprMl9lc89VXRnI+AukoqpC7vJoHDXRhcmVrVFMl4LC4WynCa/C2RIzhLf4M2NQy1I0gNih4xjukpzRwkA=="

Like other Tox clients, the Toxmail server uses this feature to convert on the fly a recipient e-mail into a corresponding Tox ID. So if I write an e-mail to, Toxmail knows where to send the message.

That breaks anonymity of course, if the Tox Ids are published on a public server, but that's another issue.

Offline mode

The biggest issue of the Toxmail project is the requirement of having both ends connected to the network when a mail is sent.

I have added a retry loop when the recipient is offline, but the mail will eventually make it only when the two sides are connected at the same time.

This is a bit of a problem when you are building an asynchronous messaging system. We started to discuss some possible solutions on the tracker and the idea came up to have a Supernode that would relay e-mails to a recipient when its back online.

In order to do it securely, the mail is encrypted using the Tox public/private keys so the supernode don't get the message in clear text. It uses the same crypto_box APIs than Tox itself, and that was really easy to add thanks to the nice PyNaCL binding, see

However, using supernodes is adding centralization to the whole system, and that's less appealing than a full decentralized system.

Another option is to use all your contacts as relays. A e-mail propagated to all your contacts has probably good chances to eventually make it to its destination.

Based on this, I have added a relay feature in Toxmail that will send around the mail and ask people to relay it.

This adds another issue though: for two nodes to exchange data, they have to be friends on Tox. So if you ask Bob to relay a message to Sarah, Bob needs to be friend with Sarah. And maybe Bob does not want you to know that he's friend with Sarah.

Ideally everyone should be able to relay e-mails anonymously - like other existing systems where data is just stored around for the recipient to come pick it.

I am not sure yet how to solve this issue, and maybe Tox is not suited to my e-mail use case.

Maybe I am just trying to reinvent BitMessage. Still digging :)