I use PM Pro on several sites. On one of them, (the bigges) I find that the perfomance when sending is very slow. (compared to other site). Sending a msg to one or two persons take almost 10 seconds.
Can it be that the log file is big? Where do I find the log file?
Can you let me know exact how many messages and announcements you have so that i can test in my side to see the performance? You can find in Dashboard > Front End PM PRO > All Messages and All Announcements
I have tested with 200000 messages without any performance hit.
Also let me know which version of the plugin you are using.
And for that url call, this is for new message notification. By default it is called every after 60 seconds for each user (it is changeable using hook).