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We often send out emails on behalf of other companies (using a modified email header) and recently we have had bouncebacks -<br />
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450 4.1.7 : Sender address rejected: unverified address: connect to domain.com[xxx.xxx.xxx.xxx<wbr />]: Connection timed out<br />
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450 4.7.1 : Recipient address rejected: Greylisting in progress<br />
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We think that we may need to get the client to add an SPF record with our details so we can send on behalf of them, but we have not had issues like this before
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We often send out emails on behalf of other companies (using a modified email header) and recently we have had bouncebacks -

450 4.1.7 : Sender address rejected: unverified address: connect to domain.com[xxx.xxx.xxx.xxx]: Connection timed out

450 4.7.1 : Recipient address rejected: Greylisting in progress

We think that we may need to get the client to add an SPF record with our details so we can send on behalf of them, but we have not had issues like this before

Emails being rejected by greylisting process when sending emails on behalf of other company

An email client, email reader or more formally mail user agent (MUA) is a computer program in the category of groupware environments used to access and manage a user's email. A web application that provides message management, composition, and reception functions may internally act as an email client; as a whole, it is commonly referred to as webmail. Likewise, email client may be referred to a piece of computer hardware or software whose primary or most visible role is to work as an email client. Email clients can also have other systems, like calendars, notes and contact managers.

Email Clients

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.