Like the title says, I'm new to self hosting world. 😀 while I was researching, I found out that many people dissuaded me to self host email server. Just too complicated and hard to manage. What other services that you think we should just go use the currently available providers in the market and why? 🙂thank you

So I have set up my own mail server 🙃 🙂. What an achievement for me 😆😅 And it was working fine till recently. It becomes really, really slow. And I checked the log and found out this. What could I do and what's the purpose of this? Is it a brute force attack? All these ips are owned by the same person/group?? Any help or pointers will be deeply appreciated