Your Deliverability Logs and Acoustic Reporting process bounce data differently. For accurate bounce categorization, rely on Acoustic Reporting—it reflects the final determination of Hard vs. Soft Bounces.

This discrepancy happens because the two systems handle bounce data at different stages:

Deliverability Logs ("Bad-Mailbox")

When an email is rejected due to an invalid, non-existent, or incorrect recipient address (5.X.X errors), our Deliverability Logs mark it as "Bad-Mailbox." These logs capture raw delivery information from the mail system—we ingest this data without modification.

Any email with a 5.X.X rejection code is marked as "Bad-Mailbox" in these logs, regardless of whether Acoustic Reporting ultimately classifies it as a Soft or Hard Bounce. Deliverability logs are generated approximately 24 hours after your mailing is sent and capture the raw delivery status.

Acoustic Reporting

Acoustic also processes asynchronous replies from recipient mail servers, which can arrive minutes or even days after the send. These replies allow Acoustic to accurately classify each contact as a Hard Bounce or Soft Bounce in the reporting interface.

This classification is used to update the suppression list for future mailings.

Pro Tip: Always use Acoustic Reporting for bounce analysis and list management decisions.

Thin lines appear due to how Outlook renders HTML, especially in older clients or the classic HTML engine. Match your background colors and use even-pixel image sizes to prevent this issue.

Recent Outlook versions or "New Outlook" reduce this issue, but here's what typically causes it:

Common causes

• Zooming in on Outlook Desktop
• Uneven image sizes (use even pixels, like 200×200)
• Forwarded emails (HTML formatting changes outside the original platform)

How to prevent this

Match background color – Set the email and content area background to the same color as the lines.

Set content block background – Avoid transparent content areas to minimize contrast.

Reference: See Microsoft's documentation on white horizontal lines in Outlook.

Keep your email background set to default white. Outlook 365 displays a black background for transparent areas.

This happens when the email background is set to transparent. Outlook 365 displays a black background instead of white for transparent areas.

Solution: Keep the email background set to default white. This ensures the email renders correctly in Outlook and other clients.

Once your email leaves Acoustic, the recipient's email client controls the formatting. Forwarding may change spacing, layouts, or styling—this is normal email client behavior.

Once an email leaves Acoustic and is delivered to an inbox, the formatting is controlled by the recipient's email client. Forwarding the email through clients like Outlook, Gmail, or Yahoo may change spacing, block layouts, or styling.

Note: Acoustic cannot control how your email renders after delivery. This is standard behavior across all email platforms.

Revert to the fully supported version of Outlook for Mac. Beta versions cause rendering issues that Acoustic cannot control.

This typically occurs when using the "New Outlook" (beta) version on Mac OS (versions 13.x or 16.x). Beta versions are not fully supported by Microsoft, and rendering issues can occur.

How to fix this: Revert to the fully supported version of Outlook for Mac. Acoustic only supports fully released versions of email clients.

A mail block occurs when the receiving server completely rejects your email. Prevent blocks by ensuring proper authentication (SPF, DKIM, DMARC), avoiding spammy content, and maintaining good sender reputation.

A mail block occurs when the receiving server completely rejects an email, preventing it from being delivered to the inbox. This usually happens because the sending IP or domain is on a block list or the email fails authentication or content checks.

Common causes

Unauthenticated Email – Emails without proper SPF, DKIM, or DMARC setup, or sent from free email addresses, may be blocked.

Spammy Content – Emails with excessive capitalization, punctuation, poor spelling, misleading subject lines, or content related to fast money, free products, adult content, gambling, or pharmaceuticals can trigger filters.

Blocks by Inbox Providers – If recipients mark your emails as spam, inbox providers may block future messages.

Custom Spam Filters – Some inboxes or individual recipients use filters that route certain emails to spam based on past behavior or specific keywords.

How to prevent mail blocks

• Ensure proper authentication with SPF, DKIM, and DMARC
• Avoid spammy content in your emails
• Keep spam complaints low and use feedback loops if available
• Encourage subscribers to add your email address or domain to their safe sender list or contacts

Low open rates result from technical issues (causing steep drops) or audience/content issues (causing gradual declines). Monitor list health, spam complaints, content engagement, and tracking setup to maintain healthy open rates.

A low open rate can result from both technical ("hard") issues and audience/content-related ("soft") issues.

Hard Issues (cause steep drops, like 40% → 0%)

Tracking Pixel or Technical Failures – If the open-tracking pixel is missing or broken, opens aren't recorded. Opens via clicks can still be counted as "implied opens."

Sudden Spam Delivery – If mailings are routed to spam across the board, open rates drop significantly.

Soft Issues (cause gradual declines)

Invalid/Bad Mailboxes – Sending to inactive or disabled addresses harms domain/IP reputation and can reduce inbox placement.

Abuse Complaints – High complaint rates (above ~0.3% per ISP) can damage sender reputation, lowering open rates.

Less Engaged Contacts – Adding new or unengaged contacts can gradually reduce open rates.

Content Changes – Changes in content may reduce subscriber engagement over time.

Deliverability Issues – ISP-specific placement problems can slowly affect opens.

Natural Engagement Variability (False Positives) – Minor month-to-month drops (5–10%) may simply reflect normal recipient disengagement rather than a system or deliverability problem.

Remember: Hard issues usually create sharp declines, while soft issues lead to gradual decreases.

Acoustic Campaign offers multiple unsubscribe methods to comply with regulations and maintain sender reputation. When a recipient opts out, they're added to your suppression list and won't receive future emails from that database.

Unsubscribe options

• One-click unsubscribe – Recipient clicks a link and is immediately opted out
• Preference center – Recipient chooses which types of emails to receive
• Webform – Recipient fills out a form to confirm opt-out
• Email reply – Recipient replies with keywords like "unsubscribe" or "remove me"
• List-Unsubscribe header – Email clients display an unsubscribe option in the email preheader

Best practices

• Include a clear unsubscribe link in every marketing email
• Process opt-out requests within 10 business days (CAN-SPAM requirement)
• Don't require login or additional steps beyond clicking the unsubscribe link
• Honor opt-outs permanently—don't re-add unsubscribed contacts

A bounce occurs when an email is rejected by the recipient's mail server, indicating deliverability issues that require monitoring to maintain a healthy email program.

A bounce occurs when an email is rejected by the recipient's mail server. This usually indicates deliverability issues and requires monitoring by the sender to maintain a healthy email program.

Soft bounces are temporary delivery failures, often caused by full inboxes, server downtime, or message size issues. They usually resolve themselves but repeated soft bounces may indicate ongoing problems.

Soft bounces are temporary delivery failures. Common causes include:

• Recipient inbox is full
• Receiving server is temporarily down
• Volume thresholds exceeded
• Message is too large
• Temporary authentication failures (e.g., DMARC-related issues)

Soft bounces often resolve themselves once the issue clears, but repeated soft bounces can indicate ongoing problems.

Hard bounces are permanent delivery failures caused by non-existent email addresses or domains. They're automatically added to suppression lists to prevent further sends to invalid addresses.

Hard bounces are permanent delivery failures. Common causes include:

• Email address does not exist
• Domain does not exist
• Any other permanent failure

Hard bounces are usually added automatically to a suppression list to prevent further sends to invalid addresses.

An out-of-stream bounce happens when an email initially appears delivered but later bounces due to recipient server delays. These may not appear in standard logs and can cause temporary reporting discrepancies. Contact Acoustic Support to request out-of-stream logs.

An out-of-stream bounce happens when an email initially appears as delivered but later bounces back due to delays on the recipient server. This can occur if the server accepts the message but later rejects it, often after the campaign metrics are already recorded.

These bounces may not appear in standard delivery logs and can temporarily cause discrepancies in reporting.

Need the logs? You can request out of stream logs by contacting Acoustic Support.

Ensure your email body width is divisible by 6 (like 600px). The vertical line isn't an actual element—it's caused by background color interaction with template width.

The vertical line is not an actual element—it's caused by the background color of an email block or column interacting with the template width.

Solution:

Ensure your email body width is divisible by 6. For example, using a width of 600px is recommended for consistent rendering.

If you use a different width, make sure it's divisible by 6 to prevent extra spacing that appears as a vertical line.

Pro Tip: Following this guideline helps the email display correctly across previews and email clients.

Use the Email Suppressed Gross metric to track all suppression reasons. Suppressed emails aren't considered undelivered because they are never sent. The platform provides gross counts only, not unique counts.

Suppressed emails aren't considered undelivered because they are never sent. To track them, use the Email Suppressed Gross metric, which aggregates all suppression reasons, including invalid domains, global or organization suppression lists, list/query/mailing-level suppression, and frequency controls.

The platform currently provides only gross counts, not unique counts.

Suppression reasons

Invalid System Email Domain – Email domain is invalid, non-existent, or contains typos

Email Restriction – Recipient excluded due to rules like mailing/query-level suppression or frequency control

Email Block – Recipient server blocks the email due to blacklisting, spam filtering, security policies, or email content

Pro Tip: Tracking these metrics helps you understand why emails aren't delivered and informs strategies to maintain deliverability.

Samsung Mail (version 6.1+) no longer supports media queries for responsive emails. Use a single header and footer in your template instead of relying on show/hide functionality.

Samsung Mail (version 6.1 and above) no longer supports media queries for responsive emails. As a result, elements meant to be hidden using "Hide on Desktop" or "Hide on Mobile" may still appear.

Emails viewed via business accounts or through services like Outlook or Hotmail can also ignore these media queries.

Recommended approach

• Use a single header and footer in your email template
• Avoid relying on show/hide functionality for Samsung Mail users

Note: This ensures consistent rendering across all email clients, including those that do not support responsive media queries.

Acoustic uses standard DKIM selector naming: spop1024 for 1024-bit keys or spop2048 for 2048-bit keys. Check your DNS TXT records or email headers to verify which selector is active.

In Acoustic, DKIM selectors follow a standard naming convention based on the key length:

• spop1024 → used when a 1024-bit DKIM key is provisioned
• spop2048 → used when a 2048-bit DKIM key is provisioned

For example, if your send domain is example.com and you are using a 1024-bit DKIM key, your full DNS TXT record name will look like:

spop1024._domainkey.example.com

How to verify your selector

• Check your domain's DNS records for TXT entries containing v=DKIM1
• The selector will appear at the beginning of the record (e.g., spop1024)
• Alternatively, you can send a test email and review the Authentication-Results header in the email to see the DKIM selector applied

Important notes:

• The selector is determined during provisioning by Acoustic's Deliverability/Provisioning team
• If your organization recently upgraded from 1024-bit to 2048-bit keys, you may see both selectors active during the transition
• Always confirm with your IT or DNS team before making changes to DNS records