If you cannot log in because the verification email is garbled, contact Ubisoft Support. Do not just say "my email is broken." Say:
"My legacy Uplay account sends emails with UTF-8 mojibake. Please reset my account's character encoding to UTF-8 or resend the verification as plain text ASCII."
Support agents have an internal tool to "re-encode" old profiles.
grep -P '\xEF\xBF\xBD' /var/log/uplay/*.log
Extract a Ubisoft (Uplay) user's email from data that contains UTF-8 encoded text safely and reliably.
The string =?UTF-8?B?...?= is technically called "Encoded-Word syntax." It is used in email headers (like the Subject line) to allow non-English characters to pass through older email servers safely.
If you see the code instead of the text, it means your email app failed to decode that string into readable text. This is often a temporary glitch in the email client software.