We have migrated our website to a new server and changed our email accounts sto Google Apps. After that, i reseted the cronjob to send emails but although I receive the emails on my gmail account, we had report from customers that they don't receive them on yahoo or hotmail accounts, not even on the spam folder.
I have added spf and dkin on the records to make sure the header contains the authentication of Google Apps.
so the logs suggest that all emails are sent, and the queue has no errors. The emails are received from gmail accounts and personal domain accoutns. After further testing, users with hotmail, windowslive and yahoo are not receiving them. I was thinking about installing smtp pro but i am not sur how this works. It needs 1 user and password (probably firstname.lastname@example.org) but we have other email accounts too (email@example.com, firstname.lastname@example.org, etc.).
Could this improve the situation?
It looks like your mailing IP address may be blacklisted by some of those email providers? That may explain the reason the emails are not received.
The SMTP Pro extension should work well and AFAIK it can work with multiple email addresses too.
You may want to consider using a third-party transactional mail provider instead of your current mailing server to ensure the highest delivery rate possible. Many transactional mail providers like SendGrid and Mailgun offer a free tier which you can try out and if you do not send more than 10,000 emails per month, they should be more than enough for your needs.