1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
|
# Message flows
This document explains at a high level some parts of chasquid's message
processing, in particular how messages flow through the system.
## Message reception
- Client connects to chasquid on the smtp or submission ports, and issues
HELO/EHLO.
- Client optionally performs STARTTLS.
- Client optionally performs AUTH.
- Check that this is done over TLS.
- Client sends MAIL FROM.
- Check SPF.
- Check connection security level.
- Client sends one or more RCPT TO.
- If the destination is remote, then the user must have authenticated.
- If the destination is local, check that the user exists.
- Client sends DATA.
- Client sends actual data, and ends it with '.'
- Parse the data contents to perform loop detection.
- If the sender is authenticated, DKIM-sign the email with the
corresponding key.
- If the sender is not authenticated, verify the DKIM signature (if the
email has one).
- Add the required headers (Received, SPF results, post-data hook output).
- Run the post-data hook. If the hook fails, return an error.
- Put it in the queue and reply success.
### Authenticated mail, and email spoofing
By default, authenticated users can send emails as any other user or domain.
For example, you can authenticate as `a@a`, and send email as `b@b`.
This is a design choice made to balance simplicity of operation and use.
Users who want to be strict about "MAIL FROM" or even "From:" validation can
add additional checks in the [post-DATA hook](hooks.md).
In the future, chasquid may get some option to be strict about it by default,
or on a per-domain or per-user basis. But for now, using a [post-DATA
hook](hooks.md) is the best way to make chasquid more strict about this.
## Queue processing
Before accepting a message:
- Create a (pseudo) random internal ID for it.
- For each recipient, use the alias database to expand it, add the results to
the list of final recipients (which may not be email).
- Save the resulting envelope (with the final recipients) to disk.
Queue processing runs asynchronously, there's a goroutine for each message
which does, in a loop:
- For each recipient which we have not delivered yet:
- Attempt delivery.
- Write to disk the results.
- If there are mails still pending, wait for some time (incrementally).
- When all the recipients have completed delivery, or enough time has passed:
- If all were successful, remove from the queue.
- If some failed, send a delivery status notification back to the sender.
|
