{{#if (exists issue.customfield_11111)}} //<!-- check if the field is filled or empty -->
{{#eq issue.customfield_11111 "m"}} //<!-- check for the specific field value "m" -->
Dear Sir
{{/eq}}
{{#eq issue.customfield_11111 "f"}} //<!-- check for the specific field value "m" -->
Dear Madam
{{/eq}}
{{else}} //<!-- if the field is empty -->
Dear Sir or Madam
{{/if}}