This metric, one of many partial measures for Universal Acceptance of domain names and email addresses, tracks the Email Address Internationalization (EAI) support on mail exchanger (MX) servers of second level domain names across participating Top Level Domains (TLDs). Currently all gTLDs are being surveyed, and other TLDs may be added later. EAI support is measured by running a quarterly survey using the TLD zone files and data available in the public DNS.
The list of surveyed servers is generated by parsing the TLD zone file and obtaining the complete list of second level domains (SLDs) in each TLD. We then check in the public DNS for existing MX records found in the SLDs and get the corresponding IP address(es) that the MX hostnames resolve to.
Each surveyed IP address is tested for EAI support by verifying if the MX server announces support of the SMTPUTF8 extension (See RFC 6531) in an EHLO command response, and checking that the server accepts the MAIL FROM command when provided internationalized email addresses with non-ASCII characters in the local part (left of the @ sign) and an internationalized domain name as A-label (ASCII mapping, e.g., xn--test) as well as U-label (using raw Unicode).
The quarterly survey results are provided in CSV format and each column is described below:
| # | Column | Description |
|---|---|---|
| 1 | Survey date | The date the EAI survey measurements was started (the survey takes a couple of days to complete). |
| 2 | TLD | The TLD (A-label form for IDN TLDs) to which the aggregated results correspond. Each quarterly report includes a summary line where the numbers correspond to the aggregated total of unique values across all TLDs where the TLD column will show an empty value. |
| 3 | MX total | The total number of MX records found for second level domains registrations under the TLD. |
| 4 | MX full EAI support | Total of MX servers found in second level domains under the TLD where all the resolving IP addresses were tested and passed all the EAI support checks. |
| 5 | MX partial EAI support | Total of MX servers found in second level domains under the TLD where at least one IP address passed all the EAI support checks, and at least one of the IP addresses failed at least one of the EA support checks. |
| 6 | MX no EAI support | Total of MX servers found in second level domains under the TLD where all the resolving IP addresses were tested and failed at least one of the EAI support checks. |
| 7 | IP total | Total number of unique IP addresses that the MX found in the TLD resolved to. |
| 8 | Unique IPs EAI passed | Total number of unique IP addresses that MX servers found in second level domains under the TLD resolved to and that passed all the EAI support checks. |
| 9 | Unique IPs EAI failed | Total number of unique IP addresses that MX servers found in second level domains under the TLD resolved to and that failed at least one of the EAI support checks. |
| 10 | Unique IPs EAI not tested | Total number of unique IP addresses that MX servers found in second level domains under the TLD resolved to but were not tested. This includes servers that refused connection from the survey or did not respond, as well as excluded or special use IP addresses. |