Nope: https://datatracker.ietf.org/doc/html/rfc5321#section-2.3.5
Only resolvable, fully-qualified domain names (FQDNs) are permitted
when domain names are used in SMTP. In other words, names that can
be resolved to MX RRs or address (i.e., A or AAAA) RRs (as discussed
in Section 5) are...