A: 100 contacts. Select up to 100 contacts in the Contacts list and choose Send email. The contacts are added to the To field and each contact receives the email separately. With more than 100 contacts selected, Send email is unavailable.
The Copy and Hidden copy fields each hold up to 150 characters of email addresses in total.
To email more than 100 contacts, select them in the Contacts list and choose Send email campaign. You can select up to 1000 contacts this way.