What does the error "Temp error 503" mean and how can it be resovled?

[greatestradioshow]

Hello,

I'm trying to import some eml files into Google Groups. In general, it works, but for some backups I get a lot of "Temp error 503" error messages.

Temp error 503. Backing off 60 seconds...attempt 10/10
503: b'' - 503
 - Giving up.

1. What is the reason for the error?
2. How can I fix the error?
3. And if I can't fix it because it is related to the eml file itself, how can I fast skip this affected files because right now it takes around 5 minutes to handle these error messages?

Thanks in advance.