FreeBSD Handbook's chapter "Electronic Mail" has section "SMTP Authentication" that dates back the times FreeBSD had not any OpenSSL version in base system. Now since we have different OpenSSL versions in different supported branches (1.0.2 for stable/11 and 1.1.1+ for stable/12) that differ in API and ABI, this section needs small correction because it's broken for stable/11 for the moment.
It's paragraph 4 suggests:
Next, edit /etc/make.conf and add the following lines:
The line "SENDMAIL_LDFLAGS=-L/usr/local/lib" should be replaced with another one:
That's because the only port's library our stock sendmail needs is really libsasl2.so. With -L/usr/local/lib buildworld process links sendmail with ports version of libcrypto what is wrong for stable/11 which needs base system version of libcrypto. The problem's solved with noted one-line change.
I'd like to see this change performed before 11.4-RELEASE coming soon.
Small correction: both current "SENDMAIL_LDFLAGS=-L/usr/local/lib" and "SENDMAIL_LDADD=-lsasl2" should be replaced with single line: