I'm Getting a 'Line Too Long' Error
Understanding why ImprovMX enforces RFC5321 line length limits.
ImprovMX occasionally rejects emails with this hard bounce message:
Line too long (see RFC5321 4.5.3.1.6) - ImprovMX What Does This Error Mean?
This error occurs when email content violates RFC5321 standards. Specifically, the specification states that text lines cannot exceed 1000 octets (not counting the leading dot duplicated for transparency).
Why ImprovMX Enforces This Rule
While some email providers ignore this requirement, ImprovMX takes a different approach. As a forwarding service, we bear responsibility for all forwarded messages. Accepting non-compliant emails risks downstream rejection, which could damage sender reputation.
By enforcing RFC compliance, ImprovMX protects its IP reputation and ensures reliable mail delivery across the email ecosystem.
Recommended Action
Senders receiving this error should verify their email formatting and headers to ensure RFC5321 compliance before attempting redelivery. This is typically a sender-side issue that needs to be resolved by the sending application or email client.
Still have questions? Feel free to reach out to our support team!