I have a survey program (limesurvey) running on my server(Apache), and SMTP email set on different servers. I want to send an email invitation to a group of people (about 10.000). Everytime I send a group of emails (20-500 emails) from the survey program (using the smtp email), during this "sending time", all pages requests to the survey program are being blocked. After it finishes sending the emails, people can see the requested page again.
I'm wondering if this is a problem from the program I use or it's a setting problem in my SMTP Emails Server or maybe settings on my Apache server?. Has anyone ran into that same problem and is there a solution for it?