Quality of contact information
Data quality is represented as special codes assigned to contact details to indicate data status, reliability, and relevance.
Delivery problem codes that reflect the quality of contact data are shown in the table below.
| Code | Name |
| 0 | No errors |
| 1 | Temporarily unavailable for delivery |
| 2 | DNS error |
| 3 | Mailbox is full |
| 4 | Message length exceeded |
| 5 | Timeout |
| 6 | Answering machine is on |
| 30 | No address specified |
| 31 | Format error |
| 32 | Address does not exist |
| 33 | Cannot be delivered |
| 34 | Delivery attempts are exhausted |
| 35 | Blocked by MTA |
| 36 | Spam complaint |
| 37 | Blocked by recipient |
| 38 | Recipient does not accept attachments |
| 39 | Non-existent domain |
| 50 | Contact in blacklist |
If the recipient's email address does not exist or is unavailable for any reason, the server returns a bounce message indicating the delivery failure. Depending on the cause, bounces are categorized as:
- Soft bounces — temporary delivery failures corresponding to delivery problem codes from 1 to 29. Messages are still sent to addresses with soft bounces. Each address has an internal counter tracking soft bounces. If there are 7 or more soft bounces within a month, the address receives code 34 (Delivery attempts are exhausted) and this address is permanently excluded from mailings. Customer email addresses with soft bounces are marked in the System with an orange indicator
. - Hard bounces — permanent delivery failures corresponding to codes from 30 and above. Addresses with hard bounces are permanently excluded from mailings. Customer email addresses with hard bounces are marked with a red indicator
.
See also a special section with information on warming up IP addresses, getting off blacklists, and other recommendations for high-quality mailings.