/**
 * SMTP Validation Utilities
 * Provides validation functions for SMTP server
 */
import { SmtpState } from '../interfaces.js';
/**
 * Detects header injection attempts in input strings
 * @param input - The input string to check
 * @param context - The context where this input is being used ('smtp-command' or 'email-header')
 * @returns true if header injection is detected, false otherwise
 */
export declare function detectHeaderInjection(input: string, context?: 'smtp-command' | 'email-header'): boolean;
/**
 * Sanitizes input by removing or escaping potentially dangerous characters
 * @param input - The input string to sanitize
 * @returns Sanitized string
 */
export declare function sanitizeInput(input: string): string;
/**
 * Validates an email address
 * @param email - Email address to validate
 * @returns Whether the email address is valid
 */
export declare function isValidEmail(email: string): boolean;
/**
 * Validates the MAIL FROM command syntax
 * @param args - Arguments string from the MAIL FROM command
 * @returns Object with validation result and extracted data
 */
export declare function validateMailFrom(args: string): {
    isValid: boolean;
    address?: string;
    params?: Record<string, string>;
    errorMessage?: string;
};
/**
 * Validates the RCPT TO command syntax
 * @param args - Arguments string from the RCPT TO command
 * @returns Object with validation result and extracted data
 */
export declare function validateRcptTo(args: string): {
    isValid: boolean;
    address?: string;
    params?: Record<string, string>;
    errorMessage?: string;
};
/**
 * Validates the EHLO command syntax
 * @param args - Arguments string from the EHLO command
 * @returns Object with validation result and extracted data
 */
export declare function validateEhlo(args: string): {
    isValid: boolean;
    hostname?: string;
    errorMessage?: string;
};
/**
 * Validates command in the current SMTP state
 * @param command - SMTP command
 * @param currentState - Current SMTP state
 * @returns Whether the command is valid in the current state
 */
export declare function isValidCommandSequence(command: string, currentState: SmtpState): boolean;
/**
 * Validates if a hostname is valid according to RFC 5321
 * @param hostname - Hostname to validate
 * @returns Whether the hostname is valid
 */
export declare function isValidHostname(hostname: string): boolean;