Following this tutorial How To Set Up a Host Name with DigitalOcean, my droplet is setup as:

Droplet IP: 1.2.3.4
Droplet name: example1

Domain: example1.com

A record name: @
A record IP: 1.2.3.4
A record: example1.com. 1800 IN A 1.2.3.4

CNAME name: *
CNAMe hostname: EXAMPLE1.COM.
CNAME: *.example1.com. 1800 IN CNAME example1.com.

$ hostname
example1

$ hostname -f
example1

$ cat /etc/hosts
127.0.0.1 localhost
127.0.0.1 example1

I know is tricky, but I will add a MX record mail1.example1.com and setup Postfix, Dovecot etc. on the same droplet.

Can I just add to /etc/hosts, something like "1.2.3.4 mail1.example1.com mail1" or that will not work?

Will I get in trouble with that DNS wildcard A record?

Thank you,
André

PS: I'm not using IPv6