update vSMTP homepage link (#3789)

- ref. https://github.com/awesome-selfhosted/awesome-selfhosted/issues/3558
- https://viridit.com/vsmtp-mail-transfer-agent/ : HTTP 404

README.md

@@ -436,7 +436,7 @@ Simple deployment of [E-mail](https://en.wikipedia.org/wiki/Email) servers, e.g.
 - [Sendmail](https://www.proofpoint.com/us/products/email-protection/open-source-email-solution) - Message transfer agent (MTA). `Sendmail` `C`
 - [Slimta](https://www.slimta.org) - Mail Transfer Library built on Python. ([Source Code](https://github.com/slimta/python-slimta)) `MIT` `Python`
 - [Stalwart SMTP](https://stalw.art/smtp) - Modern SMTP server designed with a focus on security, speed, and extensive configurability. ([Source Code](https://github.com/stalwartlabs/smtp-server)) `AGPL-3.0` `Rust`
-- [vSMTP](https://viridit.com/vsmtp-mail-transfer-agent/) - Next-gen MTA. Secured, Faster and Greener. ([Source Code](https://github.com/viridIT/vSMTP)) `GPL-3.0` `Rust`
+- [vSMTP](https://viridit.com/products/) - Next-gen MTA. Secured, Faster and Greener. ([Source Code](https://github.com/viridIT/vSMTP)) `GPL-3.0` `Rust`
 
 
 ### Communication - Email - Mailing Lists and Newsletters