If you have new IP and that IP don't have bad history, then your main issue is hotmail and Office365.
There is little bit rate limiting over next 24h period, but if you host yourself and don't send unsolicidated bulk messages, then you don't see those limits.
Some anti-spam services graylist you, that causes usually 5 minute delay for delivery.
90% spam score comes from message, sending server isn't that relevant (if you base configuration is reasonable: PTR is right, server knows it's hostname and don't EHLO himself as localhost and so on).
You can look at SpamAssassin default rulebase[1] for common rules.
90% spam score comes from message, sending server isn't that relevant (if you base configuration is reasonable: PTR is right, server knows it's hostname and don't EHLO himself as localhost and so on). You can look at SpamAssassin default rulebase[1] for common rules.
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[1] - https://spamassassin.apache.org/old/tests_3_3_x.html