Email Issues

My email provider is Network Solutions and I also use MailGun. To me, my email issues are complicated. My email was working fine, until I discovered that I was not receiving email from my website. That issue was solved. However, afterwhich, when I would send email out, it was sometimes not received. It's unpredictable. My SEO person is somewhat familiar with troubleshooting, but has yet to find a solution. Here is the last message that I receive from her: Hi Sam, Quick update on where things stand. Good news: SpamTitan is confirmed working again - I checked its activity log and it's actively blocking spam and delivering clean mail correctly. On the sending issue: Network Solutions support just completed an internal resync and reindex of the email system to address it. They've asked for a few hours for this to fully take effect. I'll test again after that - both general sending communication - and let you know the results. HELP!