To, Cc, Bcc and Reply-To in transactional e-mail: how many recipients and what each one costs

The short answer: to, cc and bcc take one address, a comma-separated list or an array, with at most 50 recipients per e-mail, counting all three. Each recipient counts as one e-mail and uses one credit. reply_to takes up to 5 addresses and uses no credits.

What each field is for

Field	Who sees it	When to use it
to	All recipients	The person the e-mail is about
cc	All recipients	Someone who should know, such as the customer's accountant
bcc	Only that recipient	A copy for your records, without the customer seeing
reply_to	Nobody, until they reply	When you want replies at another address, such as customer service

What it costs

Cost is counted per recipient, not per request. An e-mail with one to, two cc and one bcc is four e-mails and four credits. Addresses on the suppression list are removed before sending, are not charged and are listed in suppressed in the answer. More in credits and the daily limit.

One e-mail to many, or many e-mails

Situation	What to do
The same message to the customer and their accountant	One e-mail, with to and cc
A different invoice for each customer	One e-mail per customer, or a batch send with each one’s variables
News for your whole customer list	That is not transactional: it is a campaign. See e-mail marketing

Never put different customers in the same to or cc. Each would see the others’ addresses. For different customers’ data, one e-mail per customer.

Recipient errors

Reason	What it means
to_required	There is no recipient in to
invalid_recipient	Some addresses are not valid
too_many_recipients	More than 50 recipients in one e-mail
invalid_reply_to	reply_to is not valid or has more than 5 addresses
all_recipients_suppressed	Every recipient is on the suppression list: nothing is sent or charged

A reply to an invoice e-mail should reach someone. Set reply_to to a mailbox someone reads, instead of a "do not reply" address.

Want to send service e-mails without paying for suppressed recipients? See the API page.

See the API page

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