skins/<skin>/images/roundcube_logo.png
.You can set custom logo image displayed on the login page of SOGo by replacing
file sogo-logo.png
:
/usr/lib64/GNUstep/SOGo/WebServerResources/img/sogo-logo.png
/usr/lib/GNUstep/SOGo/WebServerResources/img/sogo-logo.png
/usr/local/GNUstep/Local/Library/SOGo/WebServerResources/img/sogo-logo.png
./usr/local/lib/GNUstep/SOGo/WebServerResources/img/sogo-logo.png
.