Sending unsolicited marketing emails through other ESPs creates a cascade of problems encompassing technical, legal, and reputational aspects. This practice, often termed 'proxying', involves sending emails to unconsenting recipients via a secondary ESP, offloading the negative repercussions onto that ESP. Key issues include authentication failures (SPF, DKIM, DMARC), tarnished domain reputation with providers like Google and Microsoft, potential IP blocking and blocklist placement, violations of anti-spam laws (GDPR, CAN-SPAM) leading to fines, erosion of user trust and engagement, and long-term damage to brand perception, with the added risk of 'list bombing'. Remediating these issues is costly and time-consuming.
9 marketer opinions
Sending unsolicited marketing emails through other ESPs presents significant issues. It damages sender reputation, leads to potential blacklisting, and violates anti-spam laws like GDPR and CAN-SPAM. High spam complaint rates affect deliverability across all campaigns. User trust erodes, engagement metrics decline (lower open rates, click-through rates, and higher unsubscribe rates), and email marketing ROI suffers. Remediating the damage can be costly and time-consuming, and the brand's reputation is tarnished, leading to potential long-term damage and loss of customers. Finally it can lead to list bombing.
Marketer view
Email marketer from Quora responds that unsolicited emails lead to lower open rates, click-through rates, and higher unsubscribe rates, ultimately damaging your email marketing ROI.
9 Sep 2021 - Quora
Marketer view
Marketer from Email Geeks asks if the scenario is where an ESP is sending cold emails advertising itself through a different ESP.
29 Jan 2025 - Email Geeks
3 expert opinions
Sending unsolicited marketing emails through other ESPs causes significant issues related to reputation damage and proxying. It involves sending emails to recipients who haven't requested them, offloading the negative reputation impact of spamming onto the competitor ESP. This proxying harms the reputation of the ESP being used without permission, potentially leading to blacklisting and deliverability problems for its legitimate users. Furthermore, it ultimately damages the brand's reputation, leading to negative perceptions from potential customers.
Expert view
Expert from Email Geeks explains the issue is that someone is sending mail to addresses that haven’t requested it and offloading the reputation hit for spamming onto one of their competitors.
12 Dec 2023 - Email Geeks
Expert view
Expert from Spam Resource explains that using another ESP to send unsolicited emails is a form of proxying and harms the reputation of the proxied ESP, leading to potential blacklisting and deliverability issues for the legitimate users of that ESP.
5 May 2024 - Spam Resource
4 technical articles
Sending unsolicited marketing emails through other ESPs leads to a multitude of technical and deliverability problems, as outlined by key documentation sources. It causes authentication failures (SPF, DKIM, DMARC), negatively impacts sender domain reputation with major email providers like Google, can result in IP address blocking by Microsoft's email services (Outlook, Hotmail), and potentially leads to blocklist placement with organizations like Spamhaus. These issues significantly degrade deliverability, causing emails to land in spam folders or be blocked entirely.
Technical article
Documentation from Microsoft SNDS clarifies that sending unsolicited emails can lead to IP addresses being blocked by Microsoft's email services (Outlook, Hotmail), severely affecting deliverability to those users.
9 Jan 2024 - Microsoft
Technical article
Documentation from Spamhaus explains if someone uses another ESP for cold emails, this can lead to blocklist placement because that is against Spamhaus' policy.
31 Jan 2023 - Spamhaus
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