Summary
The broad consensus from experts, marketers, and documentation is that whitelisting a tagged (plus addressed) Reply-To address generally does *not* automatically whitelist the untagged From address. Email systems typically treat plus addresses as distinct entities. While plus addressing is useful for tracking, you cannot rely on automatic whitelisting inheritance. Address book behavior varies, and some systems might not even recognize plus addresses. Furthermore, some ISPs might view plus addresses with suspicion. It's best to explicitly safelist both, test across platforms, and consider whether plus addresses are stripped.
Key findings
- Unique Treatment: Plus addresses are generally treated as unique and separate from the base address.
- No Whitelist Inheritance: Whitelisting a tagged address does not typically extend to the base address.
- Variable Recognition: Some systems may not recognize or properly handle plus addresses.
- Address Book Variance: Address book behavior differs across providers regarding plus addresses.
- Potential Reputation Bias: Some ISPs may view plus addresses with lower reputation due to their association with spam.
- Recipient Based whitelisting: Mail clients mainly safe list emails based on what they are sending to.
- No implicit relationship: RFC5322 allows plus addresses but does not define special handling or relationships between addresses.
Key considerations
- Explicit Safelisting: Explicitly safelist *both* tagged and untagged addresses.
- Cross-Platform Testing: Test deliverability across multiple email platforms.
- Platform Compatibility: Ensure your marketing platform supports plus addressing.
- Stripping Consideration: Be aware that some systems may strip plus addresses.
- Monitor deliverability: Monitor deliverability of campaigns using plus addressed emails to identify potential issues.
- Check brands stripping policies: Check if brands/companies automatically strip plus addresses.
What email marketers say
9 marketer opinions
The consensus is that whitelisting a tagged (plus addressed) Reply-To address does not guarantee that the untagged From address will also be whitelisted. Email systems generally treat plus addresses as unique and independent. While plus addressing is useful for tracking and organization, relying on automatic whitelisting inheritance is not advisable. Some systems may not recognize plus addresses, and even if they do, whitelisting behavior varies. Additionally, some ISPs might view plus addresses with lower reputation. It's best practice to explicitly safelist both tagged and untagged addresses and test across various email platforms.
Key opinions
- Unique Address Treatment: Plus addresses are generally treated as unique and distinct from their base addresses.
- No Whitelisting Inheritance: Whitelisting a plus address typically does not automatically whitelist the corresponding base address.
- Inconsistent Recognition: Some older email systems may not properly recognize or handle plus addresses.
- Variable Address Book Handling: Address book handling varies, with some systems grouping plus addresses and others treating them as separate contacts.
- ISPs may have reputation bias: Some ISPs may view plus addresses as having lower reputations than standard email addresses
Key considerations
- Explicit Safelisting: Explicitly safelist both the tagged (plus addressed) and untagged email addresses to ensure deliverability.
- Testing Across Platforms: Test email deliverability across various email platforms (Gmail, Hotmail, Yahoo, etc.) to understand how plus addresses are handled.
- Marketing Platform Compatibility: Verify that your email marketing platform supports plus addressing and handles it correctly.
- Monitor deliverability: Monitor deliverability of email campaigns using plus addresses to identify potential issues.
- Account for automatic stripping of plus addresses: Consider if plus addresses are stripped automatically by brands
Marketer view
Email marketer from Stack Overflow explains that tagged or 'plus' addresses are treated as unique addresses. Therefore, whitelisting a tagged Reply-To address (e.g., user+campaign1@example.com) will not automatically whitelist the untagged From address (e.g., user@example.com). Each address is treated independently by most systems.
26 Jul 2023 - Stack Overflow
Marketer view
Email marketer from Reddit mentions that address book handling varies. Some systems may treat plus addresses as separate contacts, while others might group them. Whitelisting behavior follows this pattern; there's no universal rule.
12 Oct 2022 - Reddit
What the experts say
3 expert opinions
Experts suggest that whitelisting a tagged Reply-To address generally doesn't extend to the untagged From address. Mail clients like Apple Mail and Microsoft Outlook typically add the recipient's address to the address book, not the original sender's. Consequently, the tagged and untagged addresses are treated as unrelated. Moreover, some companies might strip plus addresses, which further complicates whitelisting considerations.
Key opinions
- Recipient-Based Whitelisting: Mail clients primarily whitelist addresses based on the recipient, not the original sender.
- Unrelated Addresses: Tagged and untagged addresses are generally treated as unrelated, even if they share the same domain.
- Plus Address Stripping: Some companies strip plus addresses, which affects how replies and From addresses are handled.
Key considerations
- Address Book Behavior: Understand how different mail clients handle address book additions, particularly whether they prioritize recipients or senders.
- Plus Address Handling: Consider whether your recipients' mail systems strip plus addresses, which might impact deliverability and whitelisting effectiveness.
- Whitelisting Limitations: Don't assume that whitelisting a tagged address will automatically improve deliverability for the untagged address.
Expert view
Expert from Word to the Wise explains that plus addressing is acceptable, but that some brands use it for their own internal purposes. Some companies automatically strip them. This should be reviewed and taken into account when sending emails, particularly from replies and the affect it has on the 'From' email address. This has an affect on the question of whitelisting.
7 Jun 2022 - Word to the Wise
Expert view
Expert from Email Geeks shares that they don’t believe the whitelisting will cross between the tagged and untagged addresses, as they’re just unrelated addresses in the same domain.
19 Mar 2025 - Email Geeks
What the documentation says
4 technical articles
Email documentation from IETF, Google, Microsoft and Apple indicates that while plus addressing is supported, there's no inherent relationship defined between the base address and the plus address regarding whitelisting. RFC 5322 allows for '+' characters but doesn't specify special handling. Google's and Microsoft's documentation for Gmail and Outlook, respectively, don't mention whitelisting inheritance, implying separate treatment. Apple's documentation does not cover how plus addressing is handled.
Key findings
- RFC 5322 Neutrality: RFC 5322 allows '+' in email addresses but doesn't define special handling or relationships.
- Gmail/Outlook Implication: Google's and Microsoft's documentation implies separate treatment for base and plus addresses regarding whitelisting.
- Apple no coverage: Apple provides no direction of plus addressing, suggests each email is independent.
Key considerations
- Distinct Treatment Expectation: Expect email systems to treat base and plus addresses as distinct entities regarding whitelisting.
- Absence of Inheritance Assumption: Do not assume that whitelisting a plus address will automatically extend to the base address, or vice versa.
- Testing Required: Test whitelisting behavior with specific email providers to confirm how plus addresses are handled.
Technical article
Documentation from Google states that Gmail inherently supports plus addressing, allowing users to create variations of their email address by adding '+anything' before the '@' symbol. However, Google's documentation doesn't explicitly state whether whitelisting a plus address automatically extends to the base address, implying they are treated separately.
3 Mar 2023 - Google
Technical article
Documentation from Microsoft explains how to add addresses to safe sender list in Outlook. It provides options for domain or specific addresses. It does not specify any special handling of plus addresses - suggesting that they are treated as distinct entries.
13 Apr 2022 - Microsoft
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