An email sender's reputation, deliverability, and brand credibility can all be adversely impacted by a high spam complaint rate. More than one complaint per 1,000 emails is regarded as high as the industry guideline for a spam complaint rate is 0.1% or below.
Deliverability: Emails sent to Gmail, Yahoo, AOL, and other email providers may bounce or land in the spam folder.
Reputation: ISPs may reject emails from senders with a bad reputation.
Credibility of brand: Recipients may come to distrust and be disloyal to the sender's company.
