#sendmail 4 articles
/me/sendMail from an account without a mailbox can time out with 504 – and the Graph SDK retries it three more times gotchas / graph No MailboxNotEnabled error, just a 504 after ~30 s; the SDK RetryHandler repeats the non-idempotent POST up to 3×, so the button hangs ~2 min and a late success can send duplicates; check assignedPlans for an enabled… A newsletter looped over /me/sendMail is not bulk e-mail — and ACS Email is no longer the way out gotchas / graph Per-mailbox and tenant limits, bulk mail through Microsoft 365 "isn't a supported use", JSON sendMail can't set List-Unsubscribe, ACS Email retires 2028; keep Graph for personal batches, send newsletters through an ESP… A screenshot pasted into a support form is too big for /me/sendMail — shrink it client-side gotchas / graph Inline base64 attachments share a ~4 MB request budget; shrink bitmaps in a canvas, cap the total, and remember mailto: fallbacks carry no attachments at all E-mail HTML built like a web page falls apart in Outlook gotchas / graph Classic Outlook renders with Word: no flexbox, rounded corners or gradients, so white text on a gradient vanishes; tables, solid colours, literal values, a full document, and under ~102 KB for Gmail