In general, attachments are not considered appropriate for email marketing lists. As such, we do not support attachments for messages sent from the Listbox Composer.
To send an attachment to a discussion forum or newsletter where administrators send their messages via email, simply attach the file you wish to include to a message you create in your email program (like Outlook, Mac Mail, gmail, etc.)
Attachments have size limits, based on the number of subscribers receiving the message. The limits go down as the number of subscribers go up, as it is considered inappropriate to send huge amounts of traffic when doing any kind of bulk mailing.
Lists with 100 or fewer subscribers can send messages up to 10MB in size.
Lists with 100 - 500 subscribers can send messages up to 5MB in size.
Lists with more than 500 subscribers can send messages up to 2MB in size, or a maximum of 15GB in traffic, whichever is smaller.
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