Calculate recipient and attachment quota as separate units.

Separate message transactions, recipients, and attachment units

A message transaction is one submitted message record. Each unique envelope recipient across To, Cc, and Bcc consumes one recipient unit at a genuine provider-handoff attempt. Attachment units are calculated separately and added only where the channel's attachment policy applies.

Dashboard labels use quota used rather than emails sent because one message can consume several recipient and attachment units.

1 message to 1 To + 2 Cc + 7 Bcc = 1 message transaction and 10 recipient units

Calculate regular mailbox attachment units

Regular mailbox sending receives one 50 MB free attachment-delivery allowance per send. Multiply the attachment bytes in one message by its recipient count, subtract 50 MB, and charge one attachment unit per started 5 MB above the allowance.

The 50 MB allowance is shared across all recipients in that send; it is not granted once per recipient.

6 MB × 10 recipients = 60 MB; 60 MB - 50 MB = 10 MB; 10 MB ÷ 5 MB = 2 attachment units

• A 5 MB attachment sent to 10 recipients creates 50 MB of delivery volume: 10 recipient units and 0 attachment units.
• Any positive amount above a 5 MB step rounds up to the next attachment unit.
• Mailbox compose, webmail relay, and compatible mail-client relay use the regular mailbox attachment calculation.

Calculate marketing attachment units

Marketing sending has no free attachment allowance. Multiply attachment bytes per message by the campaign's eligible recipients and charge one attachment unit per started 1 MB of total delivery volume.

Queued campaign processing charges recipients incrementally while preserving the same campaign-wide rounding result.

0.5 MB × 100 recipients = 50 MB = 50 attachment units

Apply the correct channel rule

Current API and SMTP credential sending records recipient units. The mailbox attachment rule applies to hosted mailbox and compatible mail-client sending, not automatically to every credential path.

A locally blocked message consumes zero recipient and attachment units because it never reaches a genuine provider-handoff attempt. A provider rejection or deferral after the attempt remains billable.

Keep size limits separate from quota

Quota calculation does not override attachment count, decoded-size, complete-request, MIME, provider, or recipient limits. A message can fit within available quota and still be rejected by a size or safety limit before provider handoff.

Use binary megabytes as implemented: 1 MB equals 1,048,576 bytes. Estimate screens can round for display, while the final calculation uses bytes and rounds each applicable started step upward.