Sendmail problems with Raspbian Buster

"5.7.0 Authentication required" error in Thunderbird on my Macbook when trying to use Sendmail on my Pi for outgoing mail.  Also Alpine in a ssh shell would not send.

By comparing the setup with my exist PI, I eventually discovered that libsasl2-modules was not installed.

Multiple ipv4 and ipv6 addresses without /etc/network/interfaces on Raspberry Pi Raspian Buster

I decided to avoid /etc/network/interfaces with a new install on a Pi 3 and use dhcpcd.

Found searching the internet that I needed an entry in /etc/rc.local

ifconfig eth0:1 add 2001:8b0:7c:1::136
ifconfig eth0:1 90.155.48.136
ifconfig eth0:2 81.187.211.34