export interface SmtpSignature {
    /** Mail server / provider name */
    name: string;
    /** Regex strings to match against the SMTP 220 banner */
    bannerPatterns: string[];
    /** EHLO extensions commonly advertised by this server */
    ehloExtensions?: string[];
    /** Classification of the mail server */
    category: "provider" | "mta" | "relay";
}
export declare const SMTP_SIGNATURES: SmtpSignature[];
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