[meeting] 2025-07-01 core mailer beta planning

Organization and Planning:

Current state: Experimental mailer module was added to core in May 2025. It barely deserves the alpha status.
Goal: Get the mailer module to beta status before Drupal 11.3 is released in December 2025.

How:

• Coordinate the work in monthly meetings, first in July, second in August, third in September. Get all issues necessary to reach beta committed or at least RTBC by end of September.
• Use #1803948: [META] Adopt the symfony mailer component as backlog (i.e., link everything there), put the issues that are planned, in progress and done on #3523592: Mailer module roadmap: the path to beta and stable.
• The question on how the team would take decisions came up, but wasn't addressed conclusively.

Issues discussed (on the roadmap):

• #3397420: Add a way to capture mails sent through the mailer transport service during tests
• #3397418: Ensure origin headers of mails sent using the symfony-based mailer service comply to RFC5322
• #3380041: Create a new email interface that decorates symfony and #3530860: Create a new mailer service to wrap symfony mailer

There were different views as to which issues were important to tackle first, and we concluded that we needed to start by working out the requirements and strategy. After the meeting, we raised #3534136: Requirements and strategy for Core Mailer to cover that.

Issues discussed (not on the roadmap):

• Some research was done around email as SDC components. This approach has too many limitations, it's not worth pursuing.
• #3529014: Generate emails from entities using pluggable entity handlers An attempt has started to tackle the mail building activity by tying it closer to the entity system. That is still waiting for feedback from entity maintainers. It was pointed out that this represented one possible framework to assist with building emails, and there would likely be several others. These frameworks would all use the underlying core mail system that would be the initial focus of the roadmap.
• It was mentioned that as soon as the experimental mailer module ships with core, people will start playing with it. So, the it should safe to turn on and it must not result in any irreversible effects.

Next planning meeting:

• Next planning meeting takes place July 29th at 6PM UTC+2.