Error When Opening Maillog

I realize the error when I send email using account created with CWP (with domain added to CWP server in my server) the mail are never received by recipient either in inbox nor spam/junk (send a mail from my email address created in my server using CWP to my gmail email account). So I try open the maillog to look for error but then I got this error:

Fatal error: Allowed memory size of 402653184 bytes exhausted (tried to allocate 640198642 bytes) in /usr/local/cwpsrv/htdocs/resources/admin/modules/file_editor.php(1) : eval()'d code(1) : eval()'d code on line 18

when I open the file from the link given it shows a code which likely not editable or readable from inside CWP.

got any clue for this? and why I can't send email?

One thing for sure I still can receive email sended from gmail.com and live.com. so nothing wrong with receiving email.

you will need to check your maillog file, you can tail it using the following command

tail -f /var/log/maillog