Recipient limits: 10 per send.

MailViewed is built for one-to-one email and small groups, not campaigns, and two caps reflect that. Both are per send, not per day, and neither limits how many emails you track.

Compose: up to 10 recipients

An email written in the dashboard's Compose can go to 10 people at most, counting To, Cc and Bcc together, whichever mode you pick. Add an eleventh and Send is refused with Up to 10 recipients per send. Nothing goes out and your draft stays as it was; remove a recipient and send again. For a larger group, send from Gmail itself: it goes out as one group email and is tracked as one, up to 100 recipients. Past that the email still sends, but it isn't tracked.

Individual copies: 2 to 10 people

Pro's Individual copies for group emails sends each person their own copy through your Gmail, each with its own pixel, so per-person receipts are real. That's one Gmail send per person from a single click, and the cap of 10 people per send keeps that click well inside Gmail's own sending limits. One person needs no copies, so it starts at two, and the same address entered twice gets one copy.

• From Gmail: with more than 10 people in To, the extension stops before sending and says Individual copies are limited to 10 people per send. You choose Send as one group email (one message, one shared pixel, and everyone in To sees each other's address, like any normal group email) or Keep editing to split the list. If you send it as one, the email's page in your dashboard says why it went out as a shared copy.
• From Compose: pick Individual copies at two or more recipients and the same 10-recipient cap applies. Here Cc and Bcc recipients each get their own separate copy too, and Compose warns you that the To/Cc structure won't carry over.

Opens on a shared group email are counted for the email, never guessed per person; see Group emails: who exactly opened?.