Email attachments that are sent through the Ticketing service are limited to a maximum size of 10 MB.

However, many Internet email users have a size limit on the incoming attachments. Therefore we do not recommend sending attachments that are larger than 1 MB.  

Instead of sending your visitors over-sized documents, you can use the Knowledgebase feature.

The Knowledgebase feature allows you to upload documents and create articles that would help your visitors with their inquiries
By using this feature you can send links to the relevant knowledgebase documents / articles instead of sending these documents by an E-mail.