I run 7 postfix servers for a company, we have not had any major problems (that are not now fixed) but this is because of a number of reasons:
1) Clean IP addresses. This can be hit-and-miss so you might need to move service providers since it seems like some (OVH, Linode) seem more likely to have been used by spammers before. We have also held the IPs for a while. We have servers at 3 different VPS providers.
2) Making sure you setup DKIM/SPF properly. We see plenty of mail from others that doesn't align properly - accidentally or by ignorance - and it can mean very different things: GMail is quite forgiving but Yahoo (and their children) are very strict about alignment
3) Using the various tools available like mxtoolbox and the various blacklist checkers. We had a problem the other day because the parent domain was linked with Vidahosts (an old email provider) so even though the subdomains were clean, one domain didn't care and strongly greylisted us (some got through!)
4) Making sure your postfix installation is up-to-date and not fiddled with too much. Postfix includes features to retry greylisted mail and to backoff if it gets a "Too Many Requests" response from the other end.
5) Use https://www.mail-tester.com/ to check a mail sent from your domain, it can reveal all kinds of things you might not have set up correctly.
6) Understand your DMARC policy - even having one is a good idea even if it is p=quarantine
Most of all, before complaining about the large providers, think about how you would deal with SPAMmers and you might understand why they do certain things. Blocking ranges of IPs might seem harsh but is a much quicker way to deal with higher volumes than trying to filter each IP; more email can be better than less. Sending very low volumes doesn't allow you to build up a good reputation, especially since you can not trust by default on the web; greylisting (retry after 1 minute) is a reasonable way to block a lot of lazy SPAM attempts while allowing properly configured servers to get through.
1) Clean IP addresses. This can be hit-and-miss so you might need to move service providers since it seems like some (OVH, Linode) seem more likely to have been used by spammers before. We have also held the IPs for a while. We have servers at 3 different VPS providers. 2) Making sure you setup DKIM/SPF properly. We see plenty of mail from others that doesn't align properly - accidentally or by ignorance - and it can mean very different things: GMail is quite forgiving but Yahoo (and their children) are very strict about alignment 3) Using the various tools available like mxtoolbox and the various blacklist checkers. We had a problem the other day because the parent domain was linked with Vidahosts (an old email provider) so even though the subdomains were clean, one domain didn't care and strongly greylisted us (some got through!) 4) Making sure your postfix installation is up-to-date and not fiddled with too much. Postfix includes features to retry greylisted mail and to backoff if it gets a "Too Many Requests" response from the other end. 5) Use https://www.mail-tester.com/ to check a mail sent from your domain, it can reveal all kinds of things you might not have set up correctly. 6) Understand your DMARC policy - even having one is a good idea even if it is p=quarantine
Most of all, before complaining about the large providers, think about how you would deal with SPAMmers and you might understand why they do certain things. Blocking ranges of IPs might seem harsh but is a much quicker way to deal with higher volumes than trying to filter each IP; more email can be better than less. Sending very low volumes doesn't allow you to build up a good reputation, especially since you can not trust by default on the web; greylisting (retry after 1 minute) is a reasonable way to block a lot of lazy SPAM attempts while allowing properly configured servers to get through.