{"id":8207,"date":"2024-09-21T03:01:06","date_gmt":"2024-09-20T18:01:06","guid":{"rendered":"https:\/\/m365jp.net\/?p=8207"},"modified":"2024-09-21T03:06:21","modified_gmt":"2024-09-20T18:06:21","slug":"mc886603-updated-reject-multiple-from-addresses-p2-from-headers-without-a-sender-header","status":"publish","type":"post","link":"https:\/\/m365jp.net\/index.php\/2024-09-21-mc886603-updated-reject-multiple-from-addresses-p2-from-headers-without-a-sender-header","title":{"rendered":"MC886603 | (Updated) Reject multiple From addresses (P2 From headers) without a Sender header"},"content":{"rendered":"
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MC886603 | (Updated) Reject multiple From addresses (P2 From headers) without a Sender header<\/th>\n<\/tr>\n<\/tbody>\n<\/table>\n
\n\n\n\n\n\n\n\n
Classification<\/th>\nplanForChange<\/td>\n<\/tr>\n
Last Updated<\/th>\n09\/20\/2024 17:51:49<\/td>\n<\/tr>\n
Start Time<\/th>\n09\/10\/2024 00:59:11<\/td>\n<\/tr>\n
End Time<\/th>\n02\/24\/2025 08:00:00<\/td>\n<\/tr>\n
Message Content<\/th>\n\n

Updated September 20, 2024: We have updated the content. Thank you for your patience.<\/p>\n

Starting December 1st, we’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

If we see significant traffic exhibiting multiple From addresses (P2 >From headers) without a Sender header in your tenant in the month of September, we will send you a Message Center Post by October 15th alerting you and providing some sample message IDs. <\/p>\n

We are doing this to comply with RFC 5322 (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>\n

[When this will happen:]<\/p>\n

December 1st, 2024<\/p>\n

[How this affects your organization:] <\/p>\n

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 December 1st, you will get an NDR error code 550 5.1.20 \u201cMultiple From addresses are not allowed without Sender address\u2019\u201d.<\/p>\n

[What you can do to prepare:] <\/p>\n

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

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":"

MC886603 | (Updated) Reject multiple From addresses (P2 From headers) without a Sender header Classification p […]<\/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-8207","post","type-post","status-publish","format-standard","hentry","category-uncategorized"],"_links":{"self":[{"href":"https:\/\/m365jp.net\/index.php\/wp-json\/wp\/v2\/posts\/8207","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=8207"}],"version-history":[{"count":0,"href":"https:\/\/m365jp.net\/index.php\/wp-json\/wp\/v2\/posts\/8207\/revisions"}],"wp:attachment":[{"href":"https:\/\/m365jp.net\/index.php\/wp-json\/wp\/v2\/media?parent=8207"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/m365jp.net\/index.php\/wp-json\/wp\/v2\/categories?post=8207"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/m365jp.net\/index.php\/wp-json\/wp\/v2\/tags?post=8207"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}