Clamav and Spamassassin work at the system level. It does not matter what web based email, or any email client you use as long as your system is setup properly.
The developers at i-MSCP has done a TOP NOTCH job. Plugins are a snap to install and everything works great.
If by performance, you mean speed? If so they are comparable. They are both php based scripts all determined by your machines hardware and software configuration and of course connection speed for file transfers. Comparable features as well.
Only true way to know is install both of them and see which one you like the best. They are both easy as pie to install and get running. Basically upload to server in its own directory, point your browser to the directory you installed them in, log in and start testing the heck out of them ...
Good Luck
In my humble opinion, MonstaFTP is the best choice out there. Monsta does update often, so I like the active development it has.
Net2FTP is pretty good, but updates are far and few between. Also, the flash uploader is going out the window when flash gets killed off in the near future. HTML5 is the new kid on the block for apps like that ... Chrome has already stopped flash by default now and I am sure most browsers will follow.
I used pydio one time and just really wasn't that impressed with it, so I cannot say much on it.
These are only my opinions and I hope it helps ..
Good Luck
As a test you can DMZ your server IP in LAN router just to make sure port blocking is not your issue.
FYI, Gmail, Yahoo and Hotmail do allow to setup a white-list (I do not remember exactly how to do that as it has been several years since I set all that up) to receive mail from a private network. I can send to most of the major email providers since white-listing my services. Most likely, your email will be sent to the users spam box even after setting up a white-list at each service, so be aware of that ... You can also setup your IP and domain with services such as spamhaus, etc to verify you are not a spammer.
In order to send email and get recognized by the big players without the fuss, you have to pony up the dough for a business class IP ...
Good Luck
I knew the no life thing would be the ticket ... 
Let me know when and what you need from me. I am especially interested in testing 2.0 version. That is probably a little bit away. I already have a machine ready to test it ...
In the meantime, I will keep doing what I am doing now ...
Awesome. I always get excited for new major releases .... I can hardly wait ...
Thank you and keep up the great work ...
As RodNoc stated, I too use a shell and all that goodness. Grep is nice, you don't have to wade through logs, but not everyone who gets a website will be knowledgeable. I remember my days of learning (who am I kidding, I still learn something new everyday) and the internet was still in it's infancy, there were hardly any sources to search for. Now, today there are lots of sources, but the trollers on a lot of newbie based sites hating on you because you don't know ANYTHING is troubling when you are trying to learn. I was just thinking about keeping it as simple as possible for a newbie. Maybe they don't notice they have easy access to logs via ftp or within a terminal or even know what a terminal is or what ftp is for that matter. As I have stated before, I do remember those days of being totally lost. Nowadays, I am just a little lost. 
As far as OS system logs, those, of course are for the server owner, and kept in the dark.
I do have an idea, and I am just talking now, but maybe I could make something as simple as a little webpage pointing to the logs that are already placed within the users log directory and maybe script something to search logs for users. It sounds doable ..
Thank you for all your input.
Keep up the great work ...
It would be awesome to have a little more control on configuration of php.ini per user in their control panel via a GUI interface. Making it as highly configurable as would allow like changing openbase url, post_allows, etc. I know it has security risks invovled, but I started doing my own hosting because of the lack of control I could get out of my hosting provider.
Maybe this could be a paid plugin situation. I know I would pay for that and it could be another paid plugin to help development costs.
I thank you and keep up the great work ...
i-MSCP 1.3.0 Build: 20160626
Debian 8.5 updated to latest stable
PHP 5.6.24
Dovecot
Apache FPM
All latest free plugins (current versions) and all paid plugins except PHP Switcher
I have an issue with Spamassassin Plugin. It sounds similar to a a problem posted here Spamassassin not working? . I first noticed it when I rebooted my server. Mail headers are not being signed and I discovered spamass-milter was causing the issue. I had to stop the spamass-milter server manually then reload the spamassassin plugin through the imscp console and it works again.
Upon investigation, outside of an error about spamass-milter not being loaded in mail.log, I get "Could not retrieve sendmail macro "b"!. Please add it to confMILTER_MACROS_ENVRCPT for better spamassassin results" in my mail log. I have just enabled debug in imsp (sorry, I should have enabled to begin with, won't happen again) and will add what I may get from my logs when I try to recreate this.
Thank you and keep up the good work. 
I am in my mid forties and have been working with pc's since 1991. I am not a programmer per se, but I know enough to find track down issues and most importantly, I have no life, so I sit at my station with 4 pc's 3 of which run debian and dig and explore to expand my knowledge. I have extra pc's to install and test latest builds and help improve code by discovery and reporting. I am teaching myself more every day on scripting and programming some simple languages, so in time, I can contribute even more.
I am a Texan and do have a decent working knowledge of spanish, so I could help translate english/spanish issues as well.
I do thank you for the opportunity to extend my desire to help improve i-MSCP and be part of the team that has developed a great product.
Have a good one and keep up the good work.
