Typo3 kann problemlos mit mehreren Domains arbeiten. Allerdings macht RealURL mit der Standard-Konfiguration Probleme, falls man Seiten mit dem gleichen Namen anlegt. Die Lösung: in der realurl.conf die "rootpage_id" durch ein Array ersetzen.

realurl.conf ( liegt meistens im Verzeichnis typo3conf/ )

$rootPID = array(
'www.domain1.de' => '23',
'www.domain2.de' => '13',
'www.domain3.com' => '42'
);

$TYPO3_CONF_VARS['FE']['addRootLineFields'].= ',title,alias';
$TYPO3_CONF_VARS['EXTCONF']['realurl'] =
array(
    '_DEFAULT' => array(
        'init' => array(
            'enableCHashCache' => 1,
            'appendMissingSlash' => 'ifNotFile',
            'enableUrlDecodeCache' => 1,
            'enableUrlEncodeCache' => 1,
        ),
        'redirects' => array(),
        'preVars' => array(
            array(
                'GETvar' => 'no_cache',
                'valueMap' => array(
                    'nc' => 1,
                ),
                'noMatch' => 'bypass',
            ),
            array(
                'GETvar' => 'L',
                'valueMap' => array(
                    'en' => '2',
                    'de' => '1',
                ),
                'noMatch' => 'bypass',
            ),
        ),
        'pagePath' => array(
            'type' => 'user',
            'userFunc' => 'EXT:realurl/class.tx_realurl_advanced.php:&tx_realurl_advanced->main',
            'spaceCharacter' => '-',
            'languageGetVar' => 'L',
            'expireDays' => 3,
            'rootpage_id' => $rootPID[$_SERVER['HTTP_HOST']]
        ),
        'fileName' => array (
            'defaultToHTMLsuffixOnPrev'=> 1
        ),
        'fixedPostVars' => array(),
        'postVarSets' => array(
            '_DEFAULT' => array(
                // news archive parameters
                'archive' => array(
                    array(
                        'GETvar' => 'tx_ttnews[year]' ,
                        ),
                    array(
                        'GETvar' => 'tx_ttnews[month]' ,
                        'valueMap' => array(
                            'january' => '01',
                            'february' => '02',
                            'march' => '03',
                            'april' => '04',
                            'may' => '05',
                            'june' => '06',
                            'july' => '07',
                            'august' => '08',
                            'september' => '09',
                            'october' => '10',
                            'november' => '11',
                            'december' => '12',
                            )
                        ),
                    ),
                // news pagebrowser
                'browse' => array(
                    array(
                        'GETvar' => 'tx_ttnews[pointer]',
                        ),
                    ),
                // news categories
                'select_category' => array (
                    array(
                        'GETvar' => 'tx_ttnews[cat]',
                        ),
                    ),
                // news articles and searchwords
                'article' => array(
                    array(
                        'GETvar' => 'tx_ttnews[tt_news]',
                        'lookUpTable' => array(
                            'table' => 'tt_news',
                            'id_field' => 'uid',
                            'alias_field' => 'title',
                            'addWhereClause' => ' AND NOT deleted',
                            'useUniqueCache' => 1,
                            'useUniqueCache_conf' => array(
                                'strtolower' => 1,
                                'spaceCharacter' => '-',
                                ),
                            ),
                        ),
                    array(
                        'GETvar' => 'tx_ttnews[backPid]',
                    ),
                    array(
                        'GETvar' => 'tx_ttnews[swords]',
                        ),
                    ),
                ),
            ),
    ),
);