{"id":8013,"date":"2024-09-10T10:01:11","date_gmt":"2024-09-10T01:01:11","guid":{"rendered":"https:\/\/m365jp.net\/?p=8013"},"modified":"2024-09-10T10:15:42","modified_gmt":"2024-09-10T01:15:42","slug":"mc886603-reject-multiple-from-addresses-p2-from-headers-without-a-sender-header","status":"publish","type":"post","link":"https:\/\/m365jp.net\/index.php\/2024-09-10-mc886603-reject-multiple-from-addresses-p2-from-headers-without-a-sender-header","title":{"rendered":"MC886603 | Reject multiple From addresses (P2 From headers) without a Sender header"},"content":{"rendered":"<div class=\"postie-post\">\n<div>\n<hr>\n<table id=\"section\">\n<tbody>\n<tr>\n<th width=\"95%\">MC886603 | Reject multiple From addresses (P2 From headers) without a Sender header<\/th>\n<\/tr>\n<\/tbody>\n<\/table>\n<hr>\n<table id=\"data\">\n<tbody>\n<tr>\n<th>Classification<\/th>\n<td>planForChange<\/td>\n<\/tr>\n<tr>\n<th>Last Updated<\/th>\n<td>09\/10\/2024 00:59:50<\/td>\n<\/tr>\n<tr>\n<th>Start Time<\/th>\n<td>09\/10\/2024 00:59:11<\/td>\n<\/tr>\n<tr>\n<th>End Time<\/th>\n<td>12\/31\/2024 08:00:00<\/td>\n<\/tr>\n<tr>\n<th>Message Content<\/th>\n<td>\n<p style=\"margin-top:0in;margin-right:0in;margin-bottom:7.5pt;margin-left:0in\">Starting October 15th, we&#8217;re going to start gradually dropping messages that have multiple From addresses (also known as P2 From headers) without a Sender header from being sent   via Exchange Online.  <\/p>\n<p>We are doing this to comply with RFC 5322 (<a href=\"https:\/\/www.rfc-editor.org\/rfc\/rfc5322#section-3.6.2\" target=\"_blank\" rel=\"noopener\">https:\/\/www.rfc-editor.org\/rfc\/rfc5322#section-3.6.2<\/a>) which mandates the Sender header to be present and contain a single address   if the From header has more than one address. Noncompliance with this could be exploited by attackers, allowing them to impersonate a sender address by misleading the client into using the From header to determine the sender instead of the Sender header.<\/p>\n<p>  <\/p>\n<p>[When this will happen:]<\/p>\n<p>October 15, 2024<\/p>\n<p>[How this affects your organization:]  <\/p>\n<p>If email clients including devices and applications that you use to send messages, do so using multiple From addresses but without a Sender address header after October 15th, you will get an NDR error code 550 5.1.20 \u201cMultiple From addresses are not allowed   without Sender address\u2019\u201d.  <\/p>\n<p>[What you can do to prepare:]  <\/p>\n<p>When this change is in effect, if you need to send a message that has more than one email address in the From field, make sure that you have a single email address in the Sender header.  <\/p>\n<p>If you expect this change to cause any issues for your organization, please share that feedback.  <\/p>\n<\/td>\n<\/tr>\n<\/tbody>\n<\/table><\/div>\n<\/div>\n","protected":false},"excerpt":{"rendered":"<p>MC886603 | Reject multiple From addresses (P2 From headers) without a Sender header Classification planForChan [&hellip;]<\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"closed","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[1],"tags":[],"class_list":["post-8013","post","type-post","status-publish","format-standard","hentry","category-uncategorized"],"_links":{"self":[{"href":"https:\/\/m365jp.net\/index.php\/wp-json\/wp\/v2\/posts\/8013","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/m365jp.net\/index.php\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/m365jp.net\/index.php\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/m365jp.net\/index.php\/wp-json\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/m365jp.net\/index.php\/wp-json\/wp\/v2\/comments?post=8013"}],"version-history":[{"count":0,"href":"https:\/\/m365jp.net\/index.php\/wp-json\/wp\/v2\/posts\/8013\/revisions"}],"wp:attachment":[{"href":"https:\/\/m365jp.net\/index.php\/wp-json\/wp\/v2\/media?parent=8013"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/m365jp.net\/index.php\/wp-json\/wp\/v2\/categories?post=8013"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/m365jp.net\/index.php\/wp-json\/wp\/v2\/tags?post=8013"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}