my attachments are not received

Frequently people tell me that they did not receive the attachments that I reference in an email. I'm using Apple Mail in 14.1.2 (23B92). This has happened three times in the last two days with different people...and many times before with various people. The attachments are still visible in my sent folder but the recipients did not receive them. Most of the time my attachments are received. How can I fix this?