Some emails not send...

[kantze]

Hello.
I have a client that is sending emails to people all over the world. Some of them do not get the emails.
Why could this happen?

Is the ip reputation of the domain from where the emails are sent? If it is low, then some mail clients reject them?
If so, could I change domain name's mail settings in order to use a famous mail service such as mailchimp and sendgrid?

Also, is there an option to check if the email was delivered and read?