Can't send on a specific email

Good day!

I'm trying to send an email on a specific email address but it keeps on bouncing back. Below is the error message.

https://preview.redd.it/gcw277hzv25f1.png?width=650&format=png&auto=webp&s=687ce85e18b5e310727063d53cb1def6fb6602f3

https://preview.redd.it/2sonys91w25f1.png?width=709&format=png&auto=webp&s=249453a915a8f7865d27627c43e8194211cfd63a