1package smtpserver

2

3import (

4 "context"

5 "net"

6

7 "github.com/mjl-/mox/dns"

8)

9

10// checks if domain can accept email.

11// i.e. if it has no null mx record, regular mx records or resolve to an address.

12func checkMXRecords(ctx context.Context, resolver dns.Resolver, d dns.Domain) (bool, error) {

13 // Note: LookupMX can return an error and still return records.

14 mx, _, err := resolver.LookupMX(ctx, d.ASCII+".")

15 if err == nil && len(mx) == 1 && mx[0].Host == "." {

16 // Null MX record, explicit signal that remote does not accept email.

17 return false, nil

18 }

19 // Treat all errors that are not "no mx record" as temporary. E.g. timeout, malformed record, remote server error.

20 if err != nil && !dns.IsNotFound(err) {

21 return false, err

22 }

23 if len(mx) == 0 {

24 mx = []*net.MX{{Host: d.ASCII + "."}}

25 }

26 var lastErr error

27 for _, x := range mx {

28 ips, _, err := resolver.LookupIPAddr(ctx, x.Host)

29 if len(ips) > 0 {

30 return true, nil

31 }

32 if err != nil && !dns.IsNotFound(err) {

33 lastErr = err

34 }

35 }

36 return false, lastErr

37}

38