How to fix SMTP error code 5.4.1 when sending cold outreach to Office 365?

Email marketer from Hunter.io says that warming up an IP is critical. It involves starting with low email volumes and gradually increasing the volume over time. This helps establish a good sending reputation with email providers. Monitoring bounce rates and engagement metrics during the warmup process is necessary.

Email marketer from an Email Marketing Forum advises to diversify the sending infrastructure. They recommend using multiple IP addresses and domains to distribute the email volume. This helps avoid triggering spam filters due to high sending volumes from a single source. Monitoring IP and domain reputation regularly is crucial.

Email marketer from GlockApps highlights that improving overall email deliverability is crucial. This includes cleaning email lists to remove invalid or inactive addresses, segmenting audiences to send targeted messages, and warming up IP addresses to establish a positive sending reputation. They say that proper authentication (SPF, DKIM, DMARC) is critical.

Email marketer from Cold Emailing Community stresses the need to avoid spam traps. They advise using double opt-in for new subscribers and regularly cleaning the email list to remove old or inactive addresses. They say using email verification tools to identify and remove potentially problematic addresses is necessary.

Email marketer from Woodpecker highlights the need for personalization in cold outreach. They advise personalizing the subject lines and email content to make them relevant to each recipient. Using merge tags to include recipient's name and company details is essential.

Email marketer from Mailjet says that the SMTP 5.4.1 error basically means 'delivery not allowed, refused', and is typically caused by recipient-side issues such as the recipient server suspecting the incoming message to be spam, the recipient's mailbox being full, or other problems on the recipient's end.

Email marketer from Reddit emphasizes the importance of a good sending reputation. They recommend warming up the IP address, using a dedicated IP address, and sending consistent, valuable content. Good list hygiene, removing old or disengaged contacts, is also necessary.

Email marketer from Sendinblue suggests that a common cause of the 5.4.1 error is being blacklisted. They advise checking if your IP address or domain is on any blocklists using online tools. If blacklisted, they suggest following the delisting procedures for each specific blacklist.

Email marketer from Reddit suggests to focus on highly targeted outreach and personalization. He mentions building relationships with potential clients before sending cold emails. Also emphasizes the importance of complying with anti-spam laws (like GDPR and CAN-SPAM).

Expert from Email Geeks responds that she doesn’t believe their inbound filters are biased towards letting mail in from their own systems and you will encounter the same filters if you are an O365 customer mailing to other O365 senders.

Expert from Word to the Wise highlights that Microsoft's filtering is based on more than just reputation; engagement matters. Sending to unengaged users, even if they haven't complained, can lead to blocks. She recommends focusing on users who actively engage with your emails.

Expert from Email Geeks explains that the 5.4.1 error code from Outlook is basically a block at Microsoft and sounds like cold outreach mail through Google is being blocked. She suggests removing all those addresses from the list and stopping mailing them.

Expert from Email Geeks suggests stopping sending cold outreach to office365 for at least a month to see if that resets reputation enough to try again.

Expert from Spam Resource emphasizes the importance of aggressive list hygiene to maintain good deliverability. He recommends regularly removing inactive or unengaged subscribers to avoid sending to potential spam traps or users who are likely to mark emails as spam. He explains that low complaint rates and high engagement are critical for avoiding deliverability issues.

Expert from Word to the Wise explains that a 5.4.1 error often stems from poor sender reputation due to sending unsolicited emails to Microsoft's infrastructure. He emphasizes the importance of permission and targeting, warning that even purchased lists can lead to deliverability problems if recipients haven't explicitly opted in.

Expert from Email Geeks responds that sending to highly engaged contacts probably won't help, especially with B2B mail and in the context of O365. She suggests trying sender.office.com to see if the IP can be delisted. However, if it’s standard cold outreach mail going through Google, there’s no IP to delist because the block isn’t IP based.

Documentation from Microsoft Support suggests checking the sender's IP address against blocklists using online tools, verifying the sender's domain reputation, and ensuring proper SPF, DKIM, and DMARC records are configured. It also advises contacting the recipient's email administrator for assistance.

Documentation from EasyDMARC highlights that a poor sender reputation, often stemming from sending unsolicited emails, can lead to a 5.4.1 error. Improving sender reputation involves implementing email authentication protocols (SPF, DKIM, DMARC), warming up IP addresses, and segmenting email lists.

Documentation from Microsoft Support explains that the 5.4.1 error indicates a problem with the recipient's email server refusing to accept the message. This could be due to the recipient's mailbox being full, the server being unavailable, or the sending server being blocked.