1. Check your mail client software and make sure it supports the type of file you are trying to send.
2. Check your mail server and make sure it is properly configured to handle and store large files.
3. Delete older, unnecessary emails to make room for your new emails.
4. Make sure your antivirus software is up-to-date and configured properly to allow attachments to pass through.
5. Check your mail client to ensure that any email size limits are set according to company policy.