Sending email fails if domain not found.

Even though an MX address exists for sysadmininc.com, an A or AAAA record does not. The email should still be delivered.

Nov  7 02:16:16 bbs synchronet: mail 0000 SEND last_msg=9879, smb.status.last_msg=9880, elapsed=633
Nov  7 02:16:16 bbs synchronet: mail 0000 SEND Message #9879 (671 of 672) from <nigel@nigelreed.net> to '' <nigel@sysadmininc.com>
Nov  7 02:16:16 bbs synchronet: mail 0000 SEND getting message text
Nov  7 02:16:16 bbs synchronet: mail 0000 SEND using auto-detected DNS server address: 2001:4860:4860::8844
Nov  7 02:16:16 bbs synchronet: mail 0000 !SEND INVALID DNS server address: 2001:4860:4860::8844
Nov  7 02:16:16 bbs synchronet: mail 0000 SEND Message #9880 (672 of 672) from <nigel@nigelreed.net> to '' <nigel@sysadmininc.com>
Nov  7 02:16:16 bbs synchronet: mail 0000 SEND getting message text
Nov  7 02:16:16 bbs synchronet: mail 0000 SEND using auto-detected DNS server address: 8.8.8.8
Nov  7 02:16:16 bbs synchronet: mail 0000 SEND getting MX records for sysadmininc.com from 8.8.8.8
Nov  7 02:16:16 bbs synchronet: mail 0133 SEND resolving SMTP hostname: sysadmininc.com
Nov  7 02:16:16 bbs synchronet: mail 0133 SEND !Failure resolving hostname: sysadmininc.com
Nov  7 02:16:16 bbs synchronet: mail 0133 SEND !Delivery attempt #1 FAILED (Error resolving hostname sysadmininc.com) for message #9880 from nigel to nigel@sysadmininc.com

$ dig @8.8.8.8 sysadmininc.com mx +short
bbs@bbs:~$ dig @8.8.8.8 sysadmininc.com mx

; <<>> DiG 9.16.1-Ubuntu <<>> @8.8.8.8 sysadmininc.com mx
; (1 server found)
;; global options: +cmd
;; Got answer:
;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 60603
;; flags: qr rd ra ad; QUERY: 1, ANSWER: 2, AUTHORITY: 0, ADDITIONAL: 1

;; OPT PSEUDOSECTION:
; EDNS: version: 0, flags:; udp: 512
;; QUESTION SECTION:
;sysadmininc.com.               IN      MX

;; ANSWER SECTION:
sysadmininc.com.        3600    IN      MX      0 www.sysadmininc.com.
sysadmininc.com.        3600    IN      MX      10 ipv6.sysadmininc.com.

;; Query time: 55 msec
;; SERVER: 8.8.8.8#53(8.8.8.8)
;; WHEN: Sun Nov 07 02:25:39 CST 2021
;; MSG SIZE  rcvd: 85

both the MX addresses resolve fine.

This is happening when using sbbs as a relay (incoming via ipv6). Not sure about other situations.