Add Sendmail license page (fixes #1067)

[Tarekchehahde]

Summary

• Add hidden _licenses/sendmail.txt from SPDX Sendmail text.
• using examples: OpenDKIM, OpenDMARC, and OpenARC LICENSE.Sendmail files.

Test plan

• CI Build and Test (Sendmail is not OSI/FSF/OD-listed; may need maintainer guidance on catalog criteria)

Fixes #1067

Made with Cursor

[thegushi]

Hey there, thanks for this, is there anything I can do to assist moving this along?

[Tarekchehahde]

Thanks for following up — sorry for the slow reply.

The PR is still open and mergeable. It adds a hidden Sendmail catalog page using the SPDX text, with OpenDKIM / OpenDMARC / OpenARC LICENSE.Sendmail as examples.

There's nothing further needed on the license text from your side. The remaining question is maintainer policy: this site's CONTRIBUTING criteria generally look for OSI / FSF / OD listing, and Sendmail isn't on those lists (as we both noted on #1067). If maintainers want a different shape — keep it hidden, drop it, or change the examples — I'm happy to adjust.