Just wonder what if my mail server went offline for some periods, and the sending party couldn’t deliver.
Will there be any consequences except I don’t get the mail? I tried searching but they all in the perspective of a sender and get a bounce, rather the other way around.
SMTP is designed with queues and retries
Unless something has changed massively since I was deeply involved with this stuff, the people that sent you email may get a notification after some hours that their message is being delayed, and maybe after like 24-48 hours they might get a bounce. But if it’s just your SMTP server going down for an hour or two every now and then, the system should be able handle that seamlessly (barring some hiccups like messages showing up with timestamps hours in the past which sometimes is confusing).
What if longer? 6 to 8 hours per day?
The problem with this is the probability of your server being available for the next retry is fairly low.
Usually some sort of exponential backoff is used so it might retry after 5 minutes, 15 minutes, an hour, 3 hours, 6 hours, 24 hours, 48 hours, give up.
6-8 hours is probably too much for anything serious where you don’t want emails to just drop. It will work so if you’re just using it to sign up to sites and stuff, you can make sure your server is on to receive the verification emails and stuff. But I wouldn’t use it for anything important.