Hey there,
Would be happy to answer your questions
1. The banning rate of sendgrid and mailgun depends on the amount of emails sent per day/per hour, the IP through which the accounts is accessed and of course the email content if its already flagged such as flagged email subjects or links in the email body.
Sendgrid is not strict with bulk sending however, it still requires a bit of warming up in the beginning to initiate the bulk emails sending whilst mailgun requires account verification through a use case before the bulk email sending can be initiated. Mailgun would be more strict with the bounce and spam rate and can ban the accounts if these rates reach around 1-2%. If you are accessing the account through a clean good IP, the account is not usually banned then. All in all, the limit for the selected can be exhausted if these metrics are placed in check and usually these are the best practices
2. The more important thing is the inboxing rate. Now, inboxing rate would depend on two to three things which are in your control and some things which are beyond the sender's control.
- Domain warming up. We do add the domain when we deliver an account to our client however, those domains are used and would require some warming up in hitting the inbox. If you ask us to make a new customized domain for you, this would also require some domain warming up as the domain is new.
- Changing email content. The more the email content gets marked as spam, the more that domain used in that sending would start sending emails to spam, so the content needs to be changed or paraphrased constantly to hit inbox and multiple domains can be used in one account to keep it switching
- One thing that is out of sender's control is the shared IP pool through which emails are being sent from these ESPs (sendgrid or mailgun). The normal plans such as 50k-100k in both mailgun and sendgrid allows sending through shared IP pools, although they keep churning them and bringing in new IPs, if an IP has gone bad due to someone else's usage, that can impact your inboxing as well. In this regard, dedicated IP plans are available as well however, a conundrum here is that the dedicated IPs doesn't allow bulk sending immediately, it requires warming up for a week or 10 days, whilst mailgun doesn't give dedicated IP without business verification
All in all, this is a tussle between sending bulk or hitting inbox. In the middle of it, there can be reached a sweet spot where you can reach around a 50% inboxing rate by warming up initially and then sending in bulk, until the content is marked as spam.
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