Sendy supports sending emails with attachments. Although there are limits to the size of the attachments and this blog posts outlines the same.
When using Amazon SES, there are limits to the size of the attachments that you can send.
The default limit is 10mb. This is NOT enforced by Sendy. 10mb is the default attachment size supported by Amazon SES.
Here's the link that talks about it - https://docs.aws.amazon.com/ses/latest/APIReference/API_SendRawEmail.html
What happens if you try sending an email with attachment size greater than 10mb?
The campaign silently fails. On the dashboard, you will see that it has been sent to 0 receipients.
What can you do to increase the limit?
The good news is, Amazon does provide provisions for increasing the limit to 40mb. You can do it by raising a support ticket from your AWS console.
Here's the blog post about the annoucement of this new increased limit support - https://aws.amazon.com/about-aws/whats-new/2021/09/amazon-ses-emails-message-40mb/