I would like to know if it is safe to send emails with 8-bit characters or if it is still needed to use quoted-printable or base64 encoding.
The 8BITMIME extension is now 20 years old. Are there SMTP servers or mail clients that still are not 8-bit clean? Is there any impact on email deliverability when sending 8-bit emails?
I did not find any numbers but it looks like it is now quite safe to send emails with 8-bit body. But since the big players like Gmail still encode emails there might be some servers that still are not 8-bit clean.
However while sending an email with an 8-bit body might be safe, sending it with 8-bit headers is not.
RFC 2822 which was the standard until late 2008 prohibited non-ASCII characters in headers. RFC 6532 proposed a standard for 8-bit headers but it is quite recent (2012) and does not seem widely implemented yet.
So sending unencoded 8-bit emails is currently not safe.