Hi Tumic,
I seem to suffer the same issues with El Capitan / Mac Mail / Avast Free.
My problems:
1) When I get messages from my accounts: it not only takes a very, very long time to download the mails, but it also only downloads the headers - not the mail bodies. Selecting the bodies does initiate a "Download messages" but nothing happens.
2) When I switch off "Mark Mail Headers" (...not knowing what I was doing...) in Avast Settings of Mail Shield, the bodies download as well.
3) But then it only gets new messages right after the Mac Mail app has initially started. After the initial download it refuses to download more messages (I waited up to ten 10 minutes before restaring app)...
Here are my system information: OS X El Capitan 10.11.2, Mail Version 9.2 (3107), Mail host: mail.hover.com
Avast related messages in system log (extract):
Nov 25 17:28:12 server com.avast.proxy[391]: Error connecting to 192.168.0.249: Operation timed out
Nov 25 17:28:12 server com.avast.proxy[391]: Error connecting to 192.168.0.248: Operation timed out
Nov 25 17:28:12 server com.avast.proxy[391]: Error connecting to 192.168.0.246: Operation timed out
Nov 25 17:28:12 server com.avast.proxy[391]: Error connecting to 192.168.0.247: Operation timed out
Nov 25 17:28:12 server com.avast.proxy[391]: Error connecting to 192.168.0.244: Operation timed out
Nov 25 17:30:17 server com.avast.proxy[391]: Error retrieving connection address: getsockopt(): No such file or directory
Nov 25 17:30:17 server com.avast.proxy[391]: Error retrieving PID: getsockopt(): No such file or directory
Nov 25 17:30:17 server com.avast.proxy[391]: Error retrieving connection address: getsockopt(): No such file or directory
Nov 25 17:30:17 server com.avast.proxy[391]: Error retrieving PID: getsockopt(): No such file or directory
Nov 25 17:30:17 server com.avast.proxy[391]: Error retrieving connection address: getsockopt(): No such file or directory
Nov 25 17:30:17 server com.avast.proxy[391]: Error retrieving PID: getsockopt(): No such file or directory
Nov 25 17:30:17 server com.avast.proxy[391]: Error retrieving connection address: getsockopt(): No such file or directory
Nov 25 17:30:17 server com.avast.proxy[391]: Error retrieving PID: getsockopt(): No such file or directory
Nov 25 17:30:17 server com.avast.proxy[391]: Error retrieving connection address: getsockopt(): No such file or directory
Nov 25 17:30:17 server com.avast.proxy[391]: Error connecting to 192.168.0.2: Connection refused
Nov 25 17:30:17 server com.avast.proxy[391]: Error retrieving connection address: getsockopt(): No such file or directory
Nov 25 17:30:17 server com.avast.proxy[391]: Error retrieving PID: getsockopt(): No such file or directory
Nov 25 17:30:17 server com.avast.proxy[391]: Error retrieving connection address: getsockopt(): No such file or directory
Nov 25 17:30:17 server com.avast.proxy[391]: Error connecting to 192.168.0.13: Connection refused
Nov 25 17:30:17 server com.avast.proxy[391]: Error connecting to 192.168.0.3: Connection refused
Nov 25 17:30:25 server com.avast.proxy[391]: Error connecting to 2a04:f540:1::b93f:930a: connect(): No route to host
Nov 25 17:30:58 server com.avast.proxy[391]: Defective IMAP response!
Nov 25 17:30:58 server com.avast.proxy[391]: * 34 FETCH (UID 27347 MODSEQ (61369))
Nov 25 17:31:34 server com.avast.proxy[391]: Error connecting to 192.168.0.23: Operation timed out
Nov 25 17:31:34 server com.avast.proxy[391]: Error connecting to 192.168.0.20: Operation timed out
...
more..
Nov 25 17:41:43 server com.avast.proxy[391]: Error connecting to 192.168.0.253: Operation timed out
Nov 25 17:41:43 server com.avast.proxy[391]: Error connecting to 192.168.0.251: Operation timed out
Nov 25 17:41:43 server com.avast.proxy[391]: Error connecting to 192.168.0.250: Operation timed out
Nov 25 17:44:03 server com.avast.proxy[391]: Error retrieving connection address: getsockopt(): No such file or directory
Nov 25 17:44:03 server com.avast.proxy[391]: Error retrieving PID: getsockopt(): No such file or directory
Nov 25 17:44:03 server com.avast.proxy[391]: Error retrieving connection address: getsockopt(): No such file or directory
Nov 25 17:44:03 server com.avast.proxy[391]: Error retrieving PID: getsockopt(): No such file or directory
Nov 25 17:44:03 server com.avast.proxy[391]: Error retrieving connection address: getsockopt(): No such file or directory
Nov 25 17:44:03 server com.avast.proxy[391]: Error retrieving PID: getsockopt(): No such file or directory
Nov 25 17:44:03 server com.avast.proxy[391]: Error retrieving connection address: getsockopt(): No such file or directory
Nov 25 17:44:03 server com.avast.proxy[391]: Error retrieving PID: getsockopt(): No such file or directory
Nov 25 17:44:04 server com.avast.proxy[391]: Error connecting to 192.168.0.2: Connection refused
Nov 25 17:44:04 server com.avast.proxy[391]: Error retrieving connection address: getsockopt(): No such file or directory
Nov 25 17:44:04 server com.avast.proxy[391]: Error connecting to 192.168.0.18: Connection refused
Nov 25 17:44:04 server com.avast.proxy[391]: Error connecting to 192.168.0.13: Connection refused
...
This just continues permanently.
Hope this helps to solve the issue.
Tnx