This happens when attachments exceed 10 megabytes. Unfortunately, all our email servers have this limitation.

Solution: Please open an account with Dropbox, where you are able to register for free and be able to upload large files and organise them in folders with 2.5 gigabytes of space available. You will also have the ability to share the attachments to email addresses. Click on Files > FIle requests, add their email address and it sends then a link to send you files, even if they do not have a Dropbox account. The other option is a download link that you can copy and paste into an email.

Once you have your link copied and pasted in your draft, complete the email and send them the link to download the files. This is a very well used and safe way to share files without overloading your emails with heavy attachments, and you get to send to multiple recipients with ease.