You can't send attachments of any kind with campaigns or journeys. Here's why:
Email attachments are often used as a way to hide viruses and malware. Because of this, emails with attachments are more likely to get caught in spam filters, which can affect your deliverability.
Large file sizes can result in bounces from email servers with low inbox or low message size limits.
Attachments can slow down large campaign sends, as the time required to send each email is significantly greater.
Attachments take longer for recipients to download.
Alternative methods for file sharing
You can still share a file with your campaign and journey email recipients by creating and linking to a landing page in your email. It's important not to link directly to files, as some spam filters follow links and can still block your email if they find something they consider suspicious. For example, Microsoft Office files are often considered high risk.
To link to a file:
Host the file online, either on your own web server, or a cloud storage service like Google Drive, Dropbox, OneDrive or Amazon's services.
Create a landing page and use it to link to your file. Some cloud services create these pages by default when you retrieve a shareable link for that file. Alternatively, you can use a service like Unbounce.
Link to your landing page in your email.
Calendar attachments in Transactional Emails (.ics files)
We allow you to attach .ics files to Transactional emails using the 'After an appointment is created' trigger type. These files should not impede on the email's deliverability, as we have ensured the .ics file is correctly created. You have no control over the contents of the .ics file as it is automatically generated based on an algorithm we have written.