Replace swiftmailer/swiftmailer with symphony/mailer

[moudsen]

The swiftmailer/swiftmailer repository under composer has been abandoned. New library suggested is symphone/mailer.

[moudsen]

Initial thoughts using Mailer is a required refactoring of the mailGraph code to adopt Mailer. The current as-is code cannot be migrated by replacing the library only.

This will require a bit more time and testing than expected hence taking a crack at it a a later moment.

[moudsen]

Deprecation messages are appearing while debug logging for mailGraph is enabled. These messages can be safely discarded as notice and will disappear with the replacement of SwiftMailer by Mailer.

[moudsen]

https://symfony.com/doc/current/mailer.html#installation

[moudsen]

Deprecation messages are now also thrown from PHP 8.x perspective. Replacement eminent - will update on short notice to complete the deprecation lead updates required to get to a clean state again.

[moudsen]

Found some severe restrictions in using Symfony Mailer such as attaching/defining an attachment from memory. Considering PHPMailer as a replacement.

[moudsen]

Runs perfectly with PHPMailer. Abandoning Symfony from here.

composer require phpmailer/phpmailer

Comments:

• Embedding requires specific relation between images path on the server and the 'images/' reference used to build the email message (relative and absolute paths must match).

Next steps:

• Catch connection issues of SMTP from subsystem like openssl (use try/catch) -- wrong TLS setting halts the script -- server unavailable haltr the script
• Enable TLS (specifically on non-strict certificate checking)
• Enable SMTPS (setting the right parameters in combination with SMTP port)

[moudsen]

Considering abandoning the plain text output variant and use HTML only.

[moudsen]

https://informationarchitect.pl/fixed-phpmailer-and-smtp-with-ssl-issues/

[moudsen]

Template update required for html: adding "cid:" for every graph source (Swift did this for me, PHPMailer does not. Considering to tackle otherwise in the code instead of the template.

[moudsen]

Found a solution - no template change required :-). Content-id marker is now added after processing of the image attachment to the message.

[moudsen]

Depending on AutoTLS now - removing encryption configuration from config file.

[moudsen]

Error catching complete

[moudsen]

Testing and final adjustments completed. Considering to release v.212 after final code review.

[moudsen]

Found different curl behavior with PHP 8.2: cookies are automically removed after a session. Adjusted coding accordingly. Final testing rounds on Zabbix 5.4 and Zabbix 6.0 LTS in progress.

[moudsen]

Testing completed successfully. Committed as v2.12