is It possible to increase the Attachment size of e-mails sent using Email Communication Service?

Question

is It possible to increase the Attachment size of e-mails sent using Email Communication Service?

Victor Kaike 0

Recently we started to send e-mails using Communication Service, but our solution require use to send Pdf files and images into the e-mail attachment, and some of those e-mails will be bigger than 10mb, so I'm wonder;
Is it possible to increase this size?

If the answer was yes, does it also increase our billing? and also what is the maximum attachment size?
If the limit is fixed, what's the recommended pattern for sending larger files?

Thank you, this information is important for us, so we can consider our next step.

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2 answers

Your answer

Answer 1

Yes. In Azure Communication Services Email, the default total email request size limit is 10 MB, including the email body, attachments, and Base64 encoding overhead.

Key points:

Default limit
- Total email request size: 10 MB
- This includes attachments and message content.
- Because attachments are Base64 encoded, the effective usable payload is smaller. Base64 increases size by about 33%, so a practical maximum is about 7.5 MB before encoding.
Can the limit be increased?
- Yes. To send email file attachments up to 30 MB, a support request is required.
- The documentation states that quota increase requests can take up to 72 hours for evaluation and approval.
Maximum attachment size
- Without an approved increase: 10 MB total email request size.
- With an approved support request: up to 30 MB for email file attachments.
- With a 30 MB limit, Base64 overhead still applies, so the practical pre-encoding payload is lower than 30 MB.
Billing impact
- The provided documentation does not state any billing change tied specifically to increasing the attachment size limit.
Recommended pattern for larger files
- For files larger than 30 MB, the recommended approach is to store the files in Azure Blob Storage and include a link in the email.
- The files can be secured with a shared access signature (SAS) to control access.
- This is the recommended alternative for large attachments.
Related implementation note
- When sending attachments through the Email SDK, the attachment content must be read and encoded using Base64.

Answer 2

Hi,

A couple of things worth adding to the AI answer above, since they get at what you actually asked.

On billing: yes, it goes up, and it's easy to estimate. ACS Email charges $0.00025 per email plus $0.00012 per MB transferred, and Microsoft's own pricing page confirms attachments count toward that MB total. So a 10 MB email costs roughly 4x what a 1 MB email does, just from the attachment weight. That's true whether you're on the default 10 MB limit or an approved 30 MB one; the cost comes from the data itself, not from having a higher limit. (The AI answer above states billing isn't affected, that's not quite right.)

One thing to double check: the 30 MB limit is a total per-email cap (body plus all attachments combined), not per file. Worth knowing since you're attaching both PDFs and images.

On the 72-hour approval time the AI answer above mentions, That number applies to sending-rate quota requests, which is a different request type. I couldn't find a published timeline specifically for attachment-size increases, so I wouldn't count on it.

Honestly, given you're already bumping into 10 MB, I'd skip the support-request route entirely and just put the files in Blob Storage with a SAS link in the email instead. Same idea Microsoft recommends for anything over 30 MB anyway, and it keeps your emails small (cheaper), so you won't need to go back and ask for another increase later if your files grow.

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