Environment:

• Business Central Version: 28.0.4665.48837
• Connector: SMTP
• Affects: All attachments (programmatic and manual UI)

Steps to Reproduce:

1. Set up an SMTP email account in BC28
2. Open any document (e.g. Posted Sales Invoice)
3. Open Email Editor via any method
4. Add any attachment — either via UI "Add files" button or programmatically via EmailMessage.AddAttachment()
5. Click Send Email

Expected: Email arrives with attachment

Actual: Email arrives without attachment, no error shown

Diagnostic Evidence collected:

Evidence 1 — Attachment record exists correctly in table:

• Email Message Attachment table has correct record
• Email Message Id GUID matches Email Outbox Message Id
• Length field shows correct byte count (29721)
• Data field has valid Media GUID

Evidence 2 — Works in BC27, broken in BC28:

• Same code, same extension, same SMTP setup worked perfectly in BC27
• Only BC28 build 28.0.4665.48837 breaks it