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Hi Adam thanks for the response. The SP SMTP has Anonymous auth enabled plus the IP based security. I'll try the service restart to see if it helps.
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Hi Adam thanks for the response. The SP SMTP has Anonymous auth enabled plus the IP based security. I'll try the service restart to see if it helps.

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We have a Send Connector that sends all email for a specific domain to a sharepoint smtp server. This configuration has been in place for some time now but it only has one HUB Server configured as the Source Server. We would like to replace this server and add more for redundancy. <br />
<br />
Steps taken so far:<br />
Sharepoint Team confirmed they added the new HUB server IPs to the allow list<br />
Tested telnet from HUB servers. works ok<br />
Added the new servers to the Source Server tab and removed the old one.<br />
<br />
Issue is we noticed emails were starting to queue up on all HUB servers for this Send Connector in this site with the below error message. Some of the servers it queued on were not added to the source server tab for the connector.<br />
<br />
451 4.4.0 Primary target IP address responded with: “451 5.7.3 Cannot achieve Exchange Server authentication.” Attempted failover to alternate host , but that did not succeed. Either there are no alternative hosts, or delivery failed to all alternative hosts.
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We have a Send Connector that sends all email for a specific domain to a sharepoint smtp server. This configuration has been in place for some time now but it only has one HUB Server configured as the Source Server. We would like to replace this server and add more for redundancy. 

Steps taken so far:
Sharepoint Team confirmed they added the new HUB server IPs to the allow list
Tested telnet from HUB servers. works ok
Added the new servers to the Source Server tab and removed the old one.

Issue is we noticed emails were starting to queue up on all HUB servers for this Send Connector in this site with the below error message. Some of the servers it queued on were not added to the source server tab for the connector.

451 4.4.0 Primary target IP address responded with: “451 5.7.3 Cannot achieve Exchange Server authentication.” Attempted failover to alternate host , but that did not succeed. Either there are no alternative hosts, or delivery failed to all alternative hosts.

Exchange 2010 Send Connector config change error

Microsoft Sharepoint is a software platform and family of software products used for collaboration and web publishing combined. These capabilities include developing web sites, portals, intranets, content management systems, search engines, wikis, blogs, and other tools for business intelligence and collaboration. SharePoint has a Microsoft Office-like interface, and it is closely integrated with the Office suite.

Microsoft SharePoint

Exchange is the server side of a collaborative application product that is part of the Microsoft Server infrastructure. Exchange's major features include email, calendaring, contacts and tasks, support for mobile and web-based access to information, and support for data storage.

Exchange

Within Internet message handling services (MHS), a message transfer agent or mail transfer agent (MTA) or mail relay is software that transfers electronic mail messages from one computer to another using a client–server application architecture. A MTA implements both the client (sending) and server (receiving) portions of the Simple Mail Transfer Protocol (SMTP). The terms mail server, mail exchanger, and MX host may also refer to a computer performing the MTA function. The Domain Name System (DNS) associates a mail server to a domain with mail exchanger (MX) resource records containing the domain name of a host providing MTA services.